{"id":2110,"date":"2022-06-29T02:42:47","date_gmt":"2022-06-29T02:42:47","guid":{"rendered":"https:\/\/topviecit.vn\/blog\/?p=2110"},"modified":"2022-06-29T03:48:31","modified_gmt":"2022-06-29T03:48:31","slug":"cau-hoi-phong-van-javascript","status":"publish","type":"post","link":"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/","title":{"rendered":"T\u1ed5ng h\u1ee3p c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t"},"content":{"rendered":"\n<p>Javascript, HTML, CSS l\u00e0 b\u1ed9 3 ng\u00f4n ng\u1eef \u0111\u1ec9nh cao c\u1ee7a l\u1eadp tr\u00ecnh web. Tuy nhi\u00ean ng\u00f4n ng\u1eef Javascript l\u1ea1i c\u00f3 \u0111\u1eb7c th\u00f9 kh\u00e1 linh \u0111\u1ed9ng n\u00ean khi\u1ebfn nhi\u1ec1u \u1ee9ng vi\u00ean g\u1eb7p kh\u00f3 kh\u0103n trong qu\u00e1 tr\u00ecnh ph\u1ecfng v\u1ea5n. B\u00e0i vi\u1ebft d\u01b0\u1edbi \u0111\u00e2y c\u1ee7a <strong><a href=\"https:\/\/topviecit.vn\/\" target=\"_blank\" rel=\"noreferrer noopener\">topviecit.vn<\/a><\/strong> l\u00e0 t\u1ed5ng h\u1ee3p b\u1ed9 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t, \u0111\u1eebng b\u1ecf qua nh\u00e9!<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_63 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title \" >Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Tong_hop_bo_cau_hoi_phong_van_Javascript_thuong_gap_nhat\" title=\"T\u1ed5ng h\u1ee3p b\u1ed9 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t\">T\u1ed5ng h\u1ee3p b\u1ed9 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Phan_biet_giua_Null_va_Undefined\" title=\"Ph\u00e2n bi\u1ec7t gi\u1eefa Null v\u00e0 Undefined\">Ph\u00e2n bi\u1ec7t gi\u1eefa Null v\u00e0 Undefined<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Tac_dung_cua_%E2%80%9CThis%E2%80%9D_trong_javascript_la_gi\" title=\"T\u00e1c d\u1ee5ng c\u1ee7a \u201cThis\u201d trong javascript l\u00e0 g\u00ec?\">T\u00e1c d\u1ee5ng c\u1ee7a \u201cThis\u201d trong javascript l\u00e0 g\u00ec?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Diem_khac_biet_giua_var_va_let_la_gi\" title=\"\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa var v\u00e0 let l\u00e0 g\u00ec?\">\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa var v\u00e0 let l\u00e0 g\u00ec?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Diem_khac_biet_giua_va_la_gi\" title=\"\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa == v\u00e0 === l\u00e0 g\u00ec ?\">\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa == v\u00e0 === l\u00e0 g\u00ec ?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Closure_trong_javascript_la_gi_Cho_vi_du_minh_hoa\" title=\"Closure trong javascript l\u00e0 g\u00ec? Cho v\u00ed d\u1ee5 minh h\u1ecda\">Closure trong javascript l\u00e0 g\u00ec? Cho v\u00ed d\u1ee5 minh h\u1ecda<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/#Danh_sach_cac_kieu_du_lieu_nguyen_thuy_trong_ngon_ngu_javascript_la_gi\" title=\"Danh s\u00e1ch c\u00e1c ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean thu\u1ef7 trong ng\u00f4n ng\u1eef javascript l\u00e0 g\u00ec?\">Danh s\u00e1ch c\u00e1c ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean thu\u1ef7 trong ng\u00f4n ng\u1eef javascript l\u00e0 g\u00ec?<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Tong_hop_bo_cau_hoi_phong_van_Javascript_thuong_gap_nhat\"><\/span><strong>T\u1ed5ng h\u1ee3p b\u1ed9 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>N\u1ebfu b\u1ea1n \u0111ang g\u1eb7p kh\u00f3 kh\u0103n trong vi\u1ec7c chu\u1ea9n b\u1ecb ki\u1ebfn th\u1ee9c cho k\u1ef3 thi ph\u1ecfng v\u1ea5n Javascript s\u1eafp t\u1edbi, v\u1eady th\u00ec h\u00e3y tham kh\u1ea3o ngay b\u1ed9 c\u00e2u h\u1ecfi th\u01b0\u1eddng g\u1eb7p nh\u1ea5t d\u01b0\u1edbi \u0111\u00e2y nh\u00e9!<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Phan_biet_giua_Null_va_Undefined\"><\/span><strong>Ph\u00e2n bi\u1ec7t gi\u1eefa Null v\u00e0 Undefined<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ul class=\"wp-block-list\"><li>Undefined d\u1ecbch ra l\u00e0 kh\u00f4ng x\u00e1c \u0111\u1ecbnh. Trong ng\u00f4n ng\u1eef javascript, n\u1ebfu b\u1ea1n khai b\u00e1o m\u1ed9t bi\u1ebfn nh\u01b0ng kh\u00f4ng g\u00e1n gi\u00e1 tr\u1ecb cho n\u00f3, gi\u00e1 tr\u1ecb c\u1ee7a bi\u1ebfn n\u00f3 l\u00e0 kh\u00f4ng x\u00e1c \u0111\u1ecbnh hay undefined.<\/li><li>Null l\u00e0 m\u1ed9t lo\u1ea1i object nh\u01b0 c\u00e1c lo\u1ea1i object \u2018string\u2019, \u2018number\u2019,\u2026<\/li><\/ul>\n\n\n\n<p>1 typeof undefined &nbsp; \/\/&nbsp; undefined<\/p>\n\n\n\n<p>2 typeof null&nbsp; \/\/&nbsp; object<\/p>\n\n\n\n<p>Ta th\u1ea5y undefined c\u00f3 ki\u1ec3u gi\u00e1 tr\u1ecb l\u00e0 undefined, trong khi null l\u1ea1i l\u00e0 1 object. \u0110\u00e2y ch\u00ednh l\u00e0 m\u1ed9t l\u1ed7i trong JavaScript khi ta \u0111\u1ec3 ki\u1ec3u c\u1ee7a null l\u00e0 \u0111\u1ed1i t\u01b0\u1ee3ng, th\u1ef1c ch\u1ea5t n\u00f3 ph\u1ea3i l\u00e0 null.<\/p>\n\n\n\n<p>1 null === undefined \/\/ false<\/p>\n\n\n\n<p>2 null == undefined \/\/ true<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"800\" height=\"500\" src=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-16.png\" alt=\"H\u1ec7 th\u1ed1ng c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript hay g\u1eb7p \" class=\"wp-image-2112\" srcset=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-16.png 800w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-16-640x400.png 640w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-16-768x480.png 768w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><figcaption><em><em>H\u1ec7 th\u1ed1ng c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript hay g\u1eb7p\u00a0<\/em><\/em><\/figcaption><\/figure><\/div>\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Tac_dung_cua_%E2%80%9CThis%E2%80%9D_trong_javascript_la_gi\"><\/span><strong>T\u00e1c d\u1ee5ng c\u1ee7a \u201cThis\u201d trong javascript l\u00e0 g\u00ec?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u0110\u00e2y l\u00e0 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t m\u00e0 b\u1ea1n n\u00ean ghi nh\u1edb l\u1ea1i. Th\u1ef1c t\u1ebf, t\u1eeb kh\u00f3a&nbsp; \u201cthis\u201d trong javascript s\u1ebd tham chi\u1ebfu h\u01b0\u1edbng t\u1edbi \u0111\u1ed1i t\u01b0\u1ee3ng m\u00e0 n\u00f3 thu\u1ed9c v\u1ec1, \u0111\u1ed3ng ngh\u0129a \u201cthis\u201d s\u1ebd c\u00f3 gi\u00e1 tr\u1ecb kh\u00e1c nhau t\u00f9y thu\u1ed9c theo n\u01a1i m\u00e0 n\u00f3 \u0111\u01b0\u1ee3c d\u00f9ng.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>Khi \u1edf trong 1 method, \u201cthis\u201d s\u1ebd tham chi\u1ebfu \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng l\u00e0 ch\u1ee7. C\u1ee5 th\u1ec3 \u0111\u00f3 l\u00e0:<\/li><\/ul>\n\n\n\n<p>1&nbsp; var company = {<\/p>\n\n\n\n<p>2&nbsp; name: &#8220;PhongvanIT&#8221;,<\/p>\n\n\n\n<p>3&nbsp; showName: function() {<\/p>\n\n\n\n<p>4&nbsp; alert(this.name);<\/p>\n\n\n\n<p>5&nbsp; }<\/p>\n\n\n\n<p>6&nbsp; }<\/p>\n\n\n\n<p>7 company.showName();<\/p>\n\n\n\n<p>8 \/\/ K\u1ebft qu\u1ea3: &#8220;PhongvanIT&#8221;\u200b<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>Khi \u1edf trong 1 function, \u201cthis\u201d s\u1ebd tham chi\u1ebfu \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng to\u00e0n c\u1ee5c (global object). Trong web, \u201cthis\u201d s\u1ebd tham chi\u1ebfu \u0111\u1ebfn \u0111\u1ed1i t\u01b0\u1ee3ng l\u00e0 bi\u1ebfn window).<\/li><\/ul>\n\n\n\n<p>1&nbsp; var name = &#8220;GlobalObject_PhongvanIT&#8221;;<\/p>\n\n\n\n<p>2&nbsp; var showName = function(){<\/p>\n\n\n\n<p>3&nbsp; alert(this.name);<\/p>\n\n\n\n<p>4&nbsp; }<\/p>\n\n\n\n<p>5&nbsp; var company = {<\/p>\n\n\n\n<p>6&nbsp; name: &#8220;PhongvanIT&#8221;,<\/p>\n\n\n\n<p>7&nbsp; showName: function() {<\/p>\n\n\n\n<p>8&nbsp; alert(this.name);<\/p>\n\n\n\n<p>9 &nbsp; }<\/p>\n\n\n\n<p>10 }<\/p>\n\n\n\n<p>11&nbsp; company.showName();<\/p>\n\n\n\n<p>12&nbsp; \/\/ K\u1ebft qu\u1ea3: &#8220;PhongvanIT&#8221;\u200b<\/p>\n\n\n\n<p>13&nbsp; showName(); \/\/ ho\u1eb7c window.showName();<\/p>\n\n\n\n<p>14&nbsp; \/\/ K\u1ebft qu\u1ea3: &#8220;GlobalObject_PhongvanIT&#8221;\u200b<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Diem_khac_biet_giua_var_va_let_la_gi\"><\/span><strong>\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa var v\u00e0 let l\u00e0 g\u00ec?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>S\u1ef1 kh\u00e1c kh\u00e1c bi\u1ec7t gi\u1eefa var v\u00e0 let l\u00e0 \u1edf m\u1ee9c \u0111\u1ed9 ph\u1ea1m vi. N\u1ebfu Var l\u00e0 ph\u1ea1m vi function(function-scoped) th\u00ec let l\u00e0 ph\u1ea1m vi blocked (block-scoped). C\u1ee5 th\u1ec3 l\u00e0:<\/p>\n\n\n\n<p>1&nbsp; function doStuff() {<\/p>\n\n\n\n<p>2&nbsp; \/\/ c\u1ea3 a v\u00e0 b s\u1ebd c\u00f3 s\u1eb5n cho h\u00e0m n\u00e0y doStuff(), nh\u01b0ng kh\u00f4ng c\u00f3 b\u00ean ngo\u00e0i<\/p>\n\n\n\n<p>3&nbsp; let a = 5;<\/p>\n\n\n\n<p>4 &nbsp; var b = 5;<\/p>\n\n\n\n<p>5 &nbsp; console.log(a + b); \/\/ 10<\/p>\n\n\n\n<p>6 &nbsp; }<\/p>\n\n\n\n<p>7 &nbsp; doStuff(); \/\/ 10;<\/p>\n\n\n\n<p>8 &nbsp; console.log(a); \/\/ ReferenceError<\/p>\n\n\n\n<p>9 &nbsp; console.log(b); \/\/ ReferenceError<\/p>\n\n\n\n<p>10 function doMoreStuff() {<\/p>\n\n\n\n<p>11 if (2 + 2 === 4) {<\/p>\n\n\n\n<p>12 \/\/&nbsp; \u1ede \u0111\u00e2y, a s\u1ebd c\u00f3 s\u1eb5n cho to\u00e0n b\u1ed9 h\u00e0m<\/p>\n\n\n\n<p>13 var a = 5;<\/p>\n\n\n\n<p>14 \/\/ Nh\u01b0ng b s\u1ebd ch\u1ec9 kh\u1ea3 d\u1ee5ng trong kh\u1ed1i n\u00e0y<\/p>\n\n\n\n<p>15 let b = 5;<\/p>\n\n\n\n<p>16&nbsp; }<\/p>\n\n\n\n<p>17&nbsp; console.log(a); \/\/ 5<\/p>\n\n\n\n<p>18&nbsp; console.log(b); \/\/ ReferenceError<\/p>\n\n\n\n<p>19&nbsp; }<\/p>\n\n\n\n<p>20&nbsp; doMoreStuff();<\/p>\n\n\n\n<p>21&nbsp; \/\/ 5<\/p>\n\n\n\n<p>22 \/\/ ReferenceError<\/p>\n\n\n\n<p>22&nbsp; for (let i = 0; i &lt; 5; i++) {<\/p>\n\n\n\n<p>24&nbsp; \/\/ i s\u1ebd t\u0103ng l\u00ean sau m\u1ed7i l\u1ea7n l\u1eb7p<\/p>\n\n\n\n<p>25&nbsp; \/\/ v\u00e0 setTimeout s\u1ebd nh\u1eadn \u0111\u01b0\u1ee3c i m\u1edbi m\u1ed7i l\u1ea7n l\u1eb7p<\/p>\n\n\n\n<p>26 setTimeout(() =&gt; console.log(i), 100);<\/p>\n\n\n\n<p>27&nbsp; }<\/p>\n\n\n\n<p>28&nbsp; \/*<\/p>\n\n\n\n<p>29&nbsp; 1<\/p>\n\n\n\n<p>30&nbsp; 2<\/p>\n\n\n\n<p>31&nbsp; 3<\/p>\n\n\n\n<p>32&nbsp; 4<\/p>\n\n\n\n<p>33&nbsp; *\/<\/p>\n\n\n\n<p>34&nbsp; for (var j = 0; j &lt; 5; j++) {<\/p>\n\n\n\n<p>35&nbsp; \/\/ j n\u1eb1m \u1edf ph\u1ea1m vi function&nbsp;<\/p>\n\n\n\n<p>36&nbsp; \/\/ do \u0111\u00f3 n\u00f3 ko thay \u0111\u1ed5i sau m\u1ed7i l\u1ea7n l\u1eb7p&nbsp; v\u00e0&nbsp; setTimeout tr\u1ea3 ra k\u1ebft qu\u1ea3 gi\u1ed1ng nhau sau m\u1ed7i l\u1ea7n l\u1eb7p<\/p>\n\n\n\n<p>37&nbsp; setTimeout(() =&gt; console.log(j), 100);<\/p>\n\n\n\n<p>38&nbsp; }<\/p>\n\n\n\n<p>39&nbsp; *\/<\/p>\n\n\n\n<p>40&nbsp; 5<\/p>\n\n\n\n<p>42&nbsp; 5<\/p>\n\n\n\n<p>42&nbsp; 5<\/p>\n\n\n\n<p>43&nbsp; 5<\/p>\n\n\n\n<p>44&nbsp; 5<\/p>\n\n\n\n<p>45&nbsp; *\/<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Diem_khac_biet_giua_va_la_gi\"><\/span><strong>\u0110i\u1ec3m kh\u00e1c bi\u1ec7t gi\u1eefa == v\u00e0 === l\u00e0 g\u00ec ?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u201c==\u201d l\u00e0 so s\u00e1nh gi\u00e1 tr\u1ecb. C\u00f2n \u201c===\u201d l\u00e0 c\u1ea3 so s\u00e1nh gi\u00e1 tr\u1ecb v\u00e0 ki\u1ec3u d\u1eef li\u1ec7u.<\/p>\n\n\n\n<p>C\u1ee5 th\u1ec3 \u0111\u00f3 l\u00e0:<\/p>\n\n\n\n<p>1&nbsp; 1 == &#8216;1&#8217;; \/\/ true<\/p>\n\n\n\n<p>2&nbsp; 1 == [1]; \/\/ true<\/p>\n\n\n\n<p>3&nbsp; 1 == true; \/\/ true<\/p>\n\n\n\n<p>4&nbsp; 0 == &#8221;; \/\/ true<\/p>\n\n\n\n<p>5&nbsp; 0 == &#8216;0&#8217;; \/\/ true<\/p>\n\n\n\n<p>6&nbsp; 0 == false; \/\/ true<\/p>\n\n\n\n<p>Trong ng\u00f4n ng\u1eef Javascript ta kh\u00f4ng n\u00ean s\u1eed d\u1ee5ng to\u00e1n t\u1eed ==, tr\u1eeb tr\u01b0\u1eddng h\u1ee3p c\u1ea7n&nbsp; so s\u00e1nh v\u1edbi null ho\u1eb7c undefined. V\u00e0 a == null s\u1ebd tr\u1ea3 v\u1ec1 true khi&nbsp; a l\u00e0 null ho\u1eb7c undefined.<\/p>\n\n\n\n<p>1&nbsp; var a = null;<\/p>\n\n\n\n<p>2&nbsp; console.log(a == null); \/\/ true<\/p>\n\n\n\n<p>3&nbsp; console.log(a == undefined); \/\/ true<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"800\" height=\"500\" src=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-17.png\" alt=\"Trong ng\u00f4n ng\u1eef Javascript ta kh\u00f4ng n\u00ean s\u1eed d\u1ee5ng to\u00e1n t\u1eed \u201c==\u201d\" class=\"wp-image-2113\" srcset=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-17.png 800w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-17-640x400.png 640w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-17-768x480.png 768w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><figcaption><em><em>Trong ng\u00f4n ng\u1eef Javascript ta kh\u00f4ng n\u00ean s\u1eed d\u1ee5ng to\u00e1n t\u1eed \u201c==\u201d<\/em><\/em><\/figcaption><\/figure><\/div>\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Closure_trong_javascript_la_gi_Cho_vi_du_minh_hoa\"><\/span><strong>Closure trong javascript l\u00e0 g\u00ec? Cho v\u00ed d\u1ee5 minh h\u1ecda<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>Closure trong javascript l\u00e0 g\u00ec l\u00e0 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript hay xu\u1ea5t hi\u1ec7n trong b\u00e0i thi.<\/p>\n\n\n\n<p>Closure trong ng\u00f4n ng\u1eef avascript l\u00e0 m\u1ed9t h\u00e0m tham chi\u1ebfu c\u00e1c bi\u1ebfn c\u00f3 ph\u1ea1m vi v\u01b0\u1ee3t ra kh\u1ecfi ph\u1ea1m v\u1ecb h\u00e0m \u0111\u00f3. \u0110\u1ed3ng ngh\u0129a h\u00e0m n\u00e0y cho ph\u00e9p ng\u01b0\u1eddi d\u00f9ng truy c\u1eadp c\u00e1c bi\u1ebfn ho\u1eb7c tham s\u1ed1 ngo\u00e0i ph\u1ea1m vi h\u00e0m \u0111\u00f3.<\/p>\n\n\n\n<p>N\u1ebfu mu\u1ed1n s\u1eed d\u1ee5ng closure, b\u1ea1n b\u1eaft bu\u1ed9c ph\u1ea3i khai b\u00e1o 1 function b\u00ean trong 1 function kh\u00e1c n\u1eefa v\u00e0 ti\u1ebfn h\u00e0nh return n\u00f3 ra.<\/p>\n\n\n\n<p>V\u00ed d\u1ee5 minh h\u1ecda 1 l\u00e0:<\/p>\n\n\n\n<p>1&nbsp; function phongVanIT() {<\/p>\n\n\n\n<p>2&nbsp; let name = &#8216;PhongvanIT&#8217;;<\/p>\n\n\n\n<p>3&nbsp; function callName() {<\/p>\n\n\n\n<p>4&nbsp; console.log(name);<\/p>\n\n\n\n<p>5&nbsp; }<\/p>\n\n\n\n<p>6&nbsp; return callName;<\/p>\n\n\n\n<p>7 }<\/p>\n\n\n\n<p>8 var callFunc = phongVanIT();<\/p>\n\n\n\n<p>9 callFunc();<\/p>\n\n\n\n<p>10\/\/ K\u1ebft qu\u1ea3: &#8220;PhongvanIT&#8221;<\/p>\n\n\n\n<p>V\u00ed d\u1ee5 minh h\u1ecda 2:<\/p>\n\n\n\n<p>1 function phongVanIT(name) {<\/p>\n\n\n\n<p>2 return function(action){<\/p>\n\n\n\n<p>3 return action + &#8216; &#8216; + name;<\/p>\n\n\n\n<p>4 }<\/p>\n\n\n\n<p>5 }<\/p>\n\n\n\n<p>6 var hello = phongVanIT(&#8216;PhongvanIT.com&#8217;);<\/p>\n\n\n\n<p>7 var love = phongVanIT(&#8216;PhongvanIT.com&#8217;);<\/p>\n\n\n\n<p>8 console.log(hello(&#8216;Hello&#8217;)); \/\/ K\u1ebft qu\u1ea3: &#8220;Hello PhongvanIT.com&#8221;<\/p>\n\n\n\n<p>9 console.log(love(&#8216;Love&#8217;)); \/\/ K\u1ebft qu\u1ea3: &#8220;Love PhongvanIT.com&#8221;<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Danh_sach_cac_kieu_du_lieu_nguyen_thuy_trong_ngon_ngu_javascript_la_gi\"><\/span><strong>Danh s\u00e1ch c\u00e1c ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean thu\u1ef7 trong ng\u00f4n ng\u1eef javascript l\u00e0 g\u00ec?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p>\u0110\u00e2y c\u0169ng l\u00e0 m\u1ed9t c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript hay xu\u1ea5t hi\u1ec7n trong \u0111\u1ec1 thi. Ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean thu\u1ef7 trong ng\u00f4n ng\u1eef javascript kh\u00f4ng ph\u1ea3i l\u00e0 m\u1ed9t \u0111\u1ed1i t\u01b0\u1ee3ng m\u00e0 l\u00e0 m\u1ed9t ki\u1ec3u d\u1eef li\u1ec7u n\u00ean n\u00f3 kh\u00f4ng t\u1ed3n t\u1ea1i ph\u01b0\u01a1ng th\u1ee9c trong \u0111\u00f3. C\u00f3 7 ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean th\u1ee7y \u0111\u00f3 l\u00e0: Boolean, Null, Undefined, Number, BigInt, String v\u00e0 Symbol.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-18.png\" alt=\"C\u00f3 7 ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean th\u1ee7y trong Javascript\" class=\"wp-image-2114\" width=\"800\" height=\"500\" srcset=\"https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-18.png 800w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-18-640x400.png 640w, https:\/\/topviecit.vn\/blog\/wp-content\/uploads\/2022\/06\/image-18-768x480.png 768w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><figcaption><em><em>C\u00f3 7 ki\u1ec3u d\u1eef li\u1ec7u nguy\u00ean th\u1ee7y trong Javascript<\/em><\/em><\/figcaption><\/figure><\/div>\n\n\n<p>Tr\u00ean \u0111\u00e2y ch\u00fang t\u00f4i \u0111\u00e3 t\u1ed5ng h\u1ee3p cho b\u1ea1n m\u1ed9t s\u1ed1 <strong><a href=\"https:\/\/topviecit.vn\/blog\/cau-hoi-phong-van-javascript\/\">c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript<\/a><\/strong>  th\u01b0\u1eddng g\u1eb7p nh\u1ea5t. Hy v\u1ecdng ch\u00fang h\u1eefu \u00edch v\u1edbi b\u1ea1n, ch\u00fac b\u1ea1n th\u00e0nh c\u00f4ng!<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Javascript, HTML, CSS l\u00e0 b\u1ed9 3 ng\u00f4n ng\u1eef \u0111\u1ec9nh cao c\u1ee7a l\u1eadp tr\u00ecnh web. Tuy nhi\u00ean ng\u00f4n ng\u1eef Javascript l\u1ea1i c\u00f3 \u0111\u1eb7c th\u00f9 kh\u00e1 linh \u0111\u1ed9ng n\u00ean khi\u1ebfn nhi\u1ec1u \u1ee9ng vi\u00ean g\u1eb7p kh\u00f3 kh\u0103n trong qu\u00e1 tr\u00ecnh ph\u1ecfng v\u1ea5n. B\u00e0i vi\u1ebft d\u01b0\u1edbi \u0111\u00e2y c\u1ee7a topviecit.vn l\u00e0 t\u1ed5ng h\u1ee3p b\u1ed9 c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n javascript th\u01b0\u1eddng [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":2111,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"cybocfi_hide_featured_image":"","footnotes":""},"categories":[86],"tags":[460,472,473,456],"class_list":["post-2110","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-chia-se-kinh-nghiem","tag-bo-cau-hoi-phong-van","tag-cau-hoi-phong-van-javascript","tag-cau-tra-loi-phong-van","tag-kinh-nghiem-phong-van"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v24.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>T\u1ed5ng h\u1ee3p c\u00e2u h\u1ecfi ph\u1ecfng v\u1ea5n Javascript th\u01b0\u1eddng g\u1eb7p nh\u1ea5t<\/title>\n<meta name=\"description\" content=\"Javascript, HTML, CSS l\u00e0 b\u1ed9 3 ng\u00f4n ng\u1eef \u0111\u1ec9nh cao c\u1ee7a l\u1eadp tr\u00ecnh web. 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