total<\/code> l\u00e0 c\u00e1c bi\u1ebfn:<\/p>\n\n\n\nV\u00ed d\u1ee5:<\/p>\n\n\n\n
var price1 = 5;\nvar price2 = 6;\nvar total = price1 + price2;<\/code><\/pre>\n\n\n\n- Trong l\u1eadp tr\u00ecnh, gi\u1ed1ng nh\u01b0 trong \u0111\u1ea1i s\u1ed1, ch\u00fang ta s\u1eed d\u1ee5ng c\u00e1c bi\u1ebfn (gi\u1ed1ng nh\u01b0
price1<\/code>) \u0111\u1ec3 l\u01b0u gi\u1eef gi\u00e1 tr\u1ecb;<\/li>- Trong l\u1eadp tr\u00ecnh, gi\u1ed1ng nh\u01b0 trong \u0111\u1ea1i s\u1ed1, ch\u00fang ta s\u1eed d\u1ee5ng c\u00e1c bi\u1ebfn trong bi\u1ec3u th\u1ee9c (total = price1 + price2);<\/li><\/ul>\n\n\n\n
T\u1eeb v\u00ed d\u1ee5 tr\u00ean, b\u1ea1n c\u00f3 th\u1ec3 t\u00ednh ra \u0111\u01b0\u1ee3c t\u1ed5ng l\u00e0 11.<\/p>\n\n\n\n
C\u00e1c bi\u1ebfn JavaScript nh\u01b0 c\u00e1c th\u00f9ng ch\u1ee9a d\u00f9ng \u0111\u1ec3 l\u01b0u tr\u1eef gi\u00e1 tr\u1ecb d\u1eef li\u1ec7u.<\/p>\n\n\n\n
\n\n\n\n<\/span>\u0110\u1ecbnh danh trong JavaScript<\/span><\/h2>\n\n\n\nT\u1ea5t c\u1ea3 bi\u1ebfn<\/strong> trong JavaScript ph\u1ea3i \u0111\u01b0\u1ee3c \u0111\u1ecbnh danh<\/strong> v\u1edbi t\u00ean duy nh\u1ea5t<\/strong>.<\/p>\n\n\n\nNh\u1eefng t\u00ean duy nh\u1ea5t n\u00e0y \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 c\u00e1c \u0111\u1ecbnh danh<\/strong>.<\/p>\n\n\n\nC\u00e1c \u0111\u1ecbnh danh c\u00f3 th\u1ec3 l\u00e0 t\u00ean ng\u1eafn (nh\u01b0 x v\u00e0 y) ho\u1eb7c t\u00ean m\u00f4 t\u1ea3 d\u00e0i h\u01a1n (nh\u01b0 tuoi, tong, tongGiatri). <\/p>\n\n\n\n
PS: xem tr\u00ean c\u00e1c h\u1ed9i nh\u00f3m v\u1ec1 l\u1eadp tr\u00ecnh th\u00ec anh ch\u1ecb em khuy\u1ebfn kh\u00edch s\u1eed d\u1ee5ng ti\u1ebfng Anh l\u00e0m bi\u1ebfn h\u01a1n l\u00e0 ti\u1ebfng Vi\u1ec7t kh\u00f4ng d\u1ea5u, m\u1ee5c \u0111\u00edch l\u00e0 v\u00ec ph\u00f9 h\u1ee3p v\u1edbi m\u00f4i tr\u01b0\u1eddng \u0111a qu\u1ed1c gia, n\u01a1i nhi\u1ec1u c\u00f4ng ty ph\u1ea7n m\u1ec1m \u1edf VN gia c\u00f4ng cho c\u00e1c c\u00f4ng ty n\u01b0\u1edbc ngo\u00e0i. Vi\u1ec7c \u0111\u1eb7t t\u00ean bi\u1ebfn l\u00e0 ti\u1ebfng Vi\u1ec7t c\u00f3 d\u1ea5u anh em x\u1ebfp v\u00e0o d\u1ea1ng cho \u0103n d\u00e9p! Tuy nhi\u00ean th\u1ef1c t\u1ebf m\u1ed9t s\u1ed1 c\u00f4ng ty c\u1ee7a Trung Qu\u1ed1c v\u00e0 Nh\u1eadt B\u1ea3n v\u1eabn c\u00f3 l\u1eadp tr\u00ecnh vi\u00ean \u0111\u1eb7t t\u00ean bi\u1ebfn l\u00e0 ng\u00f4n ng\u1eef b\u1ea3n \u0111\u1ecba c\u1ee7a h\u1ecd trong c\u00e1c ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh n\u00f3i chung. Nh\u01b0ng v\u1ec1 \u0111\u1ea1i th\u1ec3, s\u1eed d\u1ee5ng t\u00ean bi\u1ebfn, h\u00e0m l\u00e0 ti\u1ebfng Anh v\u1eabn l\u00e0 l\u1ef1a ch\u1ecdn an to\u00e0n nh\u1ea5t.<\/p>\n\n\n\n
M\u1ed9t s\u1ed1 lu\u1eadt chung \u0111\u1ec3 x\u00e2y d\u1ef1ng t\u00ean cho c\u00e1c bi\u1ebfn (\u0111\u1ecbnh danh duy nh\u1ea5t) l\u00e0:<\/p>\n\n\n\n
- T\u00ean c\u00f3 th\u1ec3 bao g\u1ed3m ch\u1eef c\u00e1i (a, b, c,…, x, y, z), s\u1ed1 (1, 2,…, 9), k\u00fd t\u1ef1 g\u1ea1ch d\u01b0\u1edbi _ v\u00e0 k\u00fd t\u1ef1 \u0111\u00f4 la $;<\/li>
- T\u00ean ph\u1ea3i b\u1eaft \u0111\u1ea7u l\u00e0 ch\u1eef c\u00e1i, ngh\u0129a l\u00e0 t\u00ean bi\u1ebfn ki\u1ec3u 123start s\u1ebd kh\u00f4ng h\u1ee3p l\u1ec7;<\/li>
- T\u00ean c\u0169ng c\u00f3 th\u1ec3 b\u1eaft \u0111\u1ea7u v\u1edbi $ v\u00e0 _ (nh\u01b0ng ch\u00fang t\u00f4i s\u1ebd kh\u00f4ng s\u1eed d\u1ee5ng c\u00e1ch n\u00e0y trong c\u00e1c h\u01b0\u1edbng d\u1eabn v\u1ec1 JavaScript)<\/li>
- T\u00ean nh\u1ea1y c\u1ea3m v\u1edbi c\u00e1ch vi\u1ebft HOA v\u00e0 th\u01b0\u1eddng (n\u00f3i c\u00e1ch kh\u00e1c x v\u00e0 X s\u1ebd l\u00e0 2 bi\u1ebfn kh\u00e1c nhau);<\/li>
- C\u00e1c t\u1eeb \u0111\u00e3 \u0111\u01b0\u1ee3c d\u00f9ng t\u1eeb tr\u01b0\u1edbc (nh\u01b0 c\u00e1c t\u1eeb kho\u00e1 \u0111\u01b0\u1ee3c x\u00e2y d\u1ef1ng t\u1eeb tr\u01b0\u1edbc trong JavaScript) s\u1ebd kh\u00f4ng \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng l\u00e0m t\u00ean bi\u1ebfn;<\/li><\/ul>\n\n\n\n
\n\n\n\n<\/span>To\u00e1n t\u1eed g\u00e1n<\/span><\/h2>\n\n\n\nTrong JavaScript, k\u00fd hi\u1ec7u d\u1ea5u b\u1eb1ng (=<\/code>) l\u00e0 m\u1ed9t to\u00e1n t\u1eed “g\u00e1n”, kh\u00f4ng ph\u1ea3i to\u00e1n t\u1eed ch\u1ec9 s\u1ef1 “b\u1eb1ng nhau”.<\/p>\n\n\n\n\u0110i\u1ec1u n\u00e0y l\u00e0 kh\u00e1c v\u1edbi \u0111\u1ea1i s\u1ed1. V\u00ed d\u1ee5 d\u01b0\u1edbi \u0111\u00e2y kh\u00f4ng c\u00f3 \u00fd ngh\u0129a trong \u0111\u1ea1i s\u1ed1:<\/p>\n\n\n\n
x = x + 5;<\/code><\/pre>\n\n\n\nTrong JavaScript th\u00ec ng\u01b0\u1ee3c l\u1ea1i, l\u00e0 m\u1ed9t v\u00ed d\u1ee5 ho\u00e0n h\u1ea3o cho m\u1ed9t c\u00e2u l\u1ec7nh: n\u00f3 g\u00e1n gi\u00e1 tr\u1ecb x + 5 cho x.<\/p>\n\n\n\n
(N\u00f3 t\u00ednh gi\u00e1 tr\u1ecb c\u1ee7a ph\u00e9p t\u00ednh x + 5 r\u1ed3i sau \u0111\u00f3 \u0111\u1ea9y gi\u00e1 tr\u1ecb m\u1edbi n\u00e0y thay cho gi\u00e1 tr\u1ecb c\u0169 c\u1ee7a x. Gi\u00e1 tr\u1ecb c\u1ee7a x gi\u1edd \u0111\u00e2y t\u0103ng th\u00eam 5.)<\/p>\n\n\n\n
Trong JavaScript, to\u00e1n t\u1eed b\u1eb1ng \u0111\u01b0\u1ee3c vi\u1ebft nh\u01b0 th\u1ebf n\u00e0y ==<\/code><\/p>\n\n\n\n
\n\n\n\n<\/span>Ki\u1ec3u d\u1eef li\u1ec7u trong JavaScript<\/span><\/h2>\n\n\n\nC\u00e1c bi\u1ebfn trong JavaScript c\u00f3 th\u1ec3 l\u01b0u gi\u1eef gi\u00e1 tr\u1ecb s\u1ed1 thu\u1ea7n t\u00fay 100 v\u00e0 v\u0103n b\u1ea3n nh\u01b0 “Ki\u1ebfn c\u00e0ng”.<\/p>\n\n\n\n
Trong l\u1eadp tr\u00ecnh, gi\u00e1 tr\u1ecb c\u1ee7a v\u0103n b\u1ea3n \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 chu\u1ed7i (string).<\/p>\n\n\n\n
JavaScript c\u00f3 th\u1ec3 n\u1eafm gi\u1eef nhi\u1ec1u ki\u1ec3u d\u1eef li\u1ec7u kh\u00e1c nhau, nh\u01b0ng hi\u1ec7n t\u1ea1i b\u1ea1n ch\u1ec9 n\u00ean ngh\u0129 v\u1ec1 ki\u1ec3u s\u1ed1 v\u00e0 chu\u1ed7i th\u00f4i nh\u00e9.<\/p>\n\n\n\n
C\u00e1c chu\u1ed7i \u0111\u01b0\u1ee3c vi\u1ebft b\u00ean trong d\u1ea5u nh\u00e1y k\u00e9p (\"string\"<\/code>) ho\u1eb7c nh\u00e1y \u0111\u01a1n ('string'<\/code>). C\u00e1c con s\u1ed1 \u0111\u01b0\u1ee3c vi\u1ebft kh\u00f4ng c\u1ea7n d\u1ea5u nh\u00e1y.<\/p>\n\n\n\nN\u1ebfu b\u1ea1n th\u00eam d\u1ea5u nh\u00e1y quanh m\u1ed9t s\u1ed1, n\u00f3 s\u1ebd \u0111\u01b0\u1ee3c xem nh\u01b0 l\u00e0 chu\u1ed7i v\u0103n b\u1ea3n ch\u1ee9 kh\u00f4ng ph\u1ea3i l\u00e0 s\u1ed1 n\u1eefa.<\/p>\n\n\n\n
V\u00ed d\u1ee5:<\/p>\n\n\n\n
var pi = 3.14; \/\/ s\u1ed1\nvar person = \"\u0110\u1ee9c Anh\"; \/\/ chu\u1ed5i, n\u1eb1m trong nh\u00e1y k\u00e9p\nvar answer = 'D\u1ea1 v\u00e2ng!'; \/\/ chu\u1ed7i, n\u1eb1m trong nh\u00e1y \u0111\u01a1n<\/code><\/pre>\n\n\n\n
\n\n\n\n<\/span>Khai b\u00e1o (t\u1ea1o) bi\u1ebfn trong JavaScript<\/span><\/h2>\n\n\n\nT\u1ea1o bi\u1ebfn trong JavaScript \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 khai b\u00e1o bi\u1ebfn.<\/p>\n\n\n\n
B\u1ea1n khai b\u00e1o bi\u1ebfn trong JavaScript v\u1edbi t\u1eeb kho\u00e1 var<\/code>:<\/p>\n\n\n\nvar carName;<\/code><\/pre>\n\n\n\nSau khi khai b\u00e1o, bi\u1ebfn v\u1eabn ch\u01b0a c\u00f3 gi\u00e1 tr\u1ecb (theo ng\u00f4n ng\u1eef k\u1ef9 thu\u1eadt, n\u00f3 c\u00f3 gi\u00e1 tr\u1ecb kh\u00f4ng x\u00e1c \u0111\u1ecbnh<\/strong> \/ underfined<\/code>).<\/p>\n\n\n\n\u0110\u1ec3 g\u00e1n\u00a0<\/strong>m\u1ed9t gi\u00e1 tr\u1ecb cho bi\u1ebfn, b\u1ea1n s\u1eed d\u1ee5ng d\u1ea5u =<\/code> nh\u01b0 th\u1ebf n\u00e0y:<\/p>\n\n\n\ncarName = \"Volvo\";<\/code><\/pre>\n\n\n\nB\u1ea1n c\u0169ng c\u00f3 th\u1ec3 g\u00e1n gi\u00e1 tr\u1ecb cho bi\u1ebfn khi b\u1ea1n khai b\u00e1o n\u00f3:<\/p>\n\n\n\n
var carName = \"Volvo\";<\/code><\/pre>\n\n\n\nTrong v\u00ed d\u1ee5 v\u1eeba r\u1ed3i, ch\u00fang ta t\u1ea1o ra bi\u1ebfn g\u1ecdi l\u00e0 carName<\/code> v\u00e0 g\u00e1n gi\u00e1 tr\u1ecb “Volvo” cho n\u00f3.<\/p>\n\n\n\nSau \u0111\u00f3 ch\u00fang ta xu\u1ea5t gi\u00e1 tr\u1ecb n\u00e0y v\u00e0o b\u00ean trong v\u0103n b\u1ea3n HTML c\u00f3 id=\"demo\"<\/code>:<\/p>\n\n\n\nV\u00ed d\u1ee5:<\/p>\n\n\n\n
<p id=\"demo\"><\/p>\n\n<script>\n var carName = \"Volvo\";\n document.getElementById(\"demo\").innerHTML = carName;\n<\/script><\/code><\/pre>\n\n\n\nM\u1ed9t th\u00f3i quen t\u1ed1t khi l\u1eadp tr\u00ecnh \u0111\u00f3 l\u00e0 khai b\u00e1o t\u1ea5t c\u1ea3 c\u00e1c bi\u1ebfn t\u1ea1i ph\u1ea7n \u0111\u1ea7u c\u1ee7a m\u00e3.<\/p>\n\n\n\n
\n\n\n\n<\/span>M\u1ed9t c\u00e2u l\u1ec7nh, nhi\u1ec1u bi\u1ebfn<\/span><\/h2>\n\n\n\nB\u1ea1n c\u00f3 th\u1ec3 khai b\u00e1o nhi\u1ec1u bi\u1ebfn trong m\u1ed9t c\u00e2u l\u1ec7nh.<\/p>\n\n\n\n
B\u1eaft \u0111\u1ea7u c\u00e2u l\u1ec7nh v\u1edbi var<\/code>\u00a0<\/strong>v\u00e0 ph\u00e2n t\u00e1ch c\u00e1c bi\u1ebfn b\u1eb1ng d\u1ea5u ph\u1ea9y:<\/p>\n\n\n\nvar person = \"\u0110\u1ee9c Anh\", carName = \"Volvo\", price = 200;<\/code><\/pre>\n\n\n\nM\u1ed9t khai b\u00e1o c\u0169ng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c vi\u1ebft tr\u00ean nhi\u1ec1u d\u00f2ng:<\/p>\n\n\n\n
var person = \"\u0110\u1ee9c Anh\",\ncarName = \"Volvo\",\nprice = 200;<\/code><\/pre>\n\n\n\n
\n\n\n\n<\/span>Gi\u00e1 tr\u1ecb = kh\u00f4ng x\u00e1c \u0111\u1ecbnh<\/span><\/h2>\n\n\n\nTrong c\u00e1c ch\u01b0\u01a1ng tr\u00ecnh m\u00e1y t\u00ednh, c\u00e1c bi\u1ebfn th\u01b0\u1eddng \u0111\u01b0\u1ee3c khai b\u00e1o m\u00e0 kh\u00f4ng c\u00f3 gi\u00e1 tr\u1ecb. Gi\u00e1 tr\u1ecb c\u00f3 th\u1ec3 l\u00e0 c\u00e1i g\u00ec \u0111\u00f3 c\u1ea7n \u0111\u01b0\u1ee3c t\u00ednh to\u00e1n ho\u1eb7c c\u00e1i g\u00ec \u0111\u00f3 s\u1ebd \u0111\u01b0\u1ee3c cung c\u1ea5p sau b\u1edfi ng\u01b0\u1eddi d\u00f9ng nh\u1eadp v\u00e0o.<\/p>\n\n\n\n
M\u1ed9t bi\u1ebfn kh\u00f4ng \u0111\u01b0\u1ee3c khai b\u00e1o gi\u00e1 tr\u1ecb s\u1ebd c\u00f3 gi\u00e1 tr\u1ecb kh\u00f4ng x\u00e1c \u0111\u1ecbnh<\/strong> (undefined<\/code>).<\/p>\n\n\n\nBi\u1ebfn carName s\u1ebd c\u00f3 gi\u00e1 tr\u1ecb kh\u00f4ng x\u00e1c \u0111\u1ecbnh sau khi l\u1ec7nh b\u00ean d\u01b0\u1edbi \u0111\u01b0\u1ee3c th\u1ef1c thi:<\/p>\n\n\n\n
V\u00ed d\u1ee5:<\/p>\n\n\n\n
var carName;<\/code><\/pre>\n\n\n\n
\n\n\n\n<\/span>Khai b\u00e1o l\u1ea1i bi\u1ebfn trong JavaScript<\/span><\/h2>\n\n\n\nN\u1ebfu b\u1ea1n khai b\u00e1o l\u1ea1i m\u1ed9t bi\u1ebfn trong JavaScript, n\u00f3 s\u1ebd kh\u00f4ng m\u1ea5t gi\u00e1 tr\u1ecb tr\u01b0\u1edbc \u0111\u00f3 c\u1ee7a n\u00f3.<\/p>\n\n\n\n
Bi\u1ebfn carName<\/code> s\u1ebd v\u1eabn c\u00f3 gi\u00e1 tr\u1ecb l\u00e0 “Volvo” sau khi th\u1ef1c thi c\u00e1c c\u00e2u l\u1ec7nh sau:<\/p>\n\n\n\nV\u00ed d\u1ee5:<\/p>\n\n\n\n
var carName = \"Volvo\";\nvar carName;<\/code><\/pre>\n\n\n\n
\n\n\n\n<\/span>S\u1ed1 h\u1ecdc trong JavaScript<\/span><\/h2>\n\n\n\nGi\u1ed1ng nh\u01b0 \u0111\u1ea1i s\u1ed1, b\u1ea1n c\u00f3 th\u1ec3 s\u1eed d\u1ee5ng c\u00e1c ph\u00e9p t\u00ednh s\u1ed1 h\u1ecdc v\u1edbi c\u00e1c bi\u1ebfn JavaScript, s\u1eed d\u1ee5ng to\u00e1n t\u1eed =<\/code> v\u00e0 +<\/code>:<\/p>\n\n\n\nV\u00ed d\u1ee5:<\/p>\n\n\n\n
var x = 5 + 2 + 3;<\/code><\/pre>\n\n\n\nK\u1ebft qu\u1ea3 nh\u01b0 b\u1ea1n \u0111o\u00e1n \u0111\u00fang r\u1ed3i: 10 <\/strong><\/p>\n\n\n\nB\u1ea1n c\u0169ng c\u00f3 th\u1ec3 th\u00eam chu\u1ed7i, nh\u01b0ng chu\u1ed7i s\u1ebd n\u1ed1i ti\u1ebfp nhau (th\u00eam v\u00e0o ph\u1ea7n cu\u1ed1i):<\/p>\n\n\n\n
V\u00ed d\u1ee5:<\/p>\n\n\n\n
var x = \"\u0110\u1ee9c\" + \" \" + \"Anh\";<\/code><\/pre>\n\n\n\nTh\u1eed th\u00eam v\u00ed d\u1ee5 n\u00e0y n\u1eefa:<\/p>\n\n\n\n
V\u00ed d\u1ee5:<\/p>\n\n\n\n
var x = \"5\" + 2 + 3;<\/code><\/pre>\n\n\n\nB\u1ea1n \u0111o\u00e1n k\u1ebft qu\u1ea3 s\u1ebd l\u00e0 bao nhi\u00eau, kh\u00f4ng ph\u1ea3i 10 \u0111\u00e2u nh\u00e9, v\u00ec “5” l\u00e0 chu\u1ed7i r\u1ed3i, kh\u00f4ng ph\u1ea3i s\u1ed1.<\/p>\n\n\n\n
K\u1ebft qu\u1ea3 h\u01a1i b\u1ea5t ng\u1edd m\u1ed9t ch\u00fat: 523<\/strong><\/p>\n\n\n\nL\u01b0u \u00fd<\/strong>: N\u1ebfu b\u1ea1n th\u00eam m\u1ed9t s\u1ed1 v\u00e0o chu\u1ed7i, s\u1ed1 \u0111\u00f3 \u0111\u01b0\u1ee3c xem nh\u01b0 chu\u1ed7i v\u00e0 \u0111\u01b0\u1ee3c n\u1ed1i v\u00e0o cu\u1ed1i c\u1ee7a chu\u1ed7i.<\/p>\n\n\n\n<\/span>K\u00fd hi\u1ec7u \u0111\u00f4 la $ trong JavaScript<\/span><\/h2>\n\n\n\nC\u1ea7n nh\u1edb r\u1eb1ng c\u00e1c \u0111\u1ecbnh danh c\u1ee7a JavaScript ph\u1ea3i b\u1eaft \u0111\u1ea7u v\u1edbi:<\/p>\n\n\n\n
- Ch\u1eef c\u00e1i A – Z ho\u1eb7c a – z<\/li>
- K\u00fd hi\u1ec7u \u0111\u00f4 la $<\/li>
- Ho\u1eb7c d\u1ea5u g\u1ea1ch d\u01b0\u1edbi _<\/li><\/ul>\n\n\n\n
Do JS xem k\u00fd hi\u1ec7u \u0111\u00f4 la nh\u01b0 m\u1ed9t k\u00fd t\u1ef1 th\u00f4ng th\u01b0\u1eddng, c\u00e1c khai b\u00e1o bao g\u1ed3m $ l\u00e0 t\u00ean bi\u1ebfn h\u1ee3p l\u1ec7:<\/p>\n\n\n\n
var $$$ = \"Xin ch\u00e0o anh em\";\nvar $ = 2; \nvar $myMoney = 100000; \/\/ gi\u1ea5c m\u01a1 c\u1ee7a t\u00f4i :))<\/code><\/pre>\n\n\n\nS\u1eed d\u1ee5ng k\u00fd hi\u1ec7u \u0111\u00f4 l\u00e0 l\u00e0 \u0111i\u1ec1u r\u1ea5t hi\u1ebfm g\u1eb7p trong JavaScript, nh\u01b0ng c\u00e1c l\u1eadp tr\u00ecnh vi\u00ean chuy\u00ean nghi\u1ec7p th\u01b0\u1eddng s\u1eed d\u1ee5ng n\u00f3 \u0111\u1ec3 l\u00e0m b\u00ed danh cho m\u1ed9t h\u00e0m ch\u00ednh trong th\u01b0 vi\u1ec7n JS c\u1ee7a h\u1ecd.<\/p>\n\n\n\n
V\u00ed d\u1ee5 trong th\u01b0 vi\u1ec7n JS jQuery, h\u00e0m ch\u00ednh $ \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 l\u1ef1a ch\u1ecdn c\u00e1c ph\u1ea7n t\u1eed HTML. Trong jQuery $(\"p\");<\/code> c\u00f3 ngh\u0129a l\u00e0 “l\u1ef1a ch\u1ecdn t\u1ea5t c\u1ea3 c\u00e1c ph\u1ea7n t\u1eed p”.<\/p>\n\n\n\n<\/span>K\u00fd hi\u1ec7u g\u1ea1ch d\u01b0\u1edbi trong JavaScript<\/span><\/h2>\n\n\n\nJS v\u1edbi k\u00fd hi\u1ec7u g\u1ea1ch d\u01b0\u1edbi nh\u01b0 m\u1ed9t k\u00fd t\u1ef1, c\u00e1c khai b\u00e1o bao g\u1ed3m d\u1ea5u g\u1ea1ch d\u01b0\u1edbi _ l\u00e0 bi\u1ebfn h\u1ee3p l\u1ec7, v\u00ed d\u1ee5:<\/p>\n\n\n\n
var _lastName = \"Nguy\u1ec5n\";\nvar _x = 2;\nvar _100 = 10;<\/code><\/pre>\n\n\n\nS\u1eed d\u1ee5ng g\u1ea1ch d\u01b0\u1edbi c\u0169ng r\u1ea5t hi\u1ebfm g\u1eb7p trong JavaScript, nh\u01b0ng c\u00f3 m\u1ecdt quy \u01b0\u1edbc gi\u1eefa c\u00e1c l\u1eadp tr\u00ecnh vi\u00ean chuy\u00ean nghi\u1ec7p \u0111\u00f3 l\u00e0 s\u1eed d\u1ee5ng n\u00f3 l\u00e0m b\u00ed danh cho c\u00e1c bi\u1ebfn “ri\u00eang t\u01b0 (\u1ea9n)”.<\/p>\n","protected":false},"excerpt":{"rendered":"
C\u00f3 3 c\u00e1ch \u0111\u1ec3 khai b\u00e1o bi\u1ebfn trong JavaScript: S\u1eed d\u1ee5ng var; S\u1eed d\u1ee5ng let; S\u1eed d\u1ee5ng const; B\u00e0i vi\u1ebft n\u00e0y s\u1ebd ch\u1ec9 n\u00f3i v\u1ec1 c\u00e1ch s\u1eed d\u1ee5ng var, v\u1ec1 let v\u00e0 const s\u1ebd \u0111\u01b0\u1ee3c n\u00f3i trong c\u00e1c b\u00e0i vi\u1ebft kh\u00e1c. Bi\u1ebfn trong JavaScript d\u00f9ng \u0111\u1ec3 ch\u1ee9a gi\u00e1 tr\u1ecb d\u1eef li\u1ec7u. Trong v\u00ed d\u1ee5 b\u00ean …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[236],"tags":[],"yoast_head":"\n
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