Prior to theECMAScript 2015 (ES6)language specification that today’s JavaScript is based on, there was only one way to declare a variable — using thevarkeyword. As a result, most older code and learning resources will only usevarfor variables. We’ll go over the differences betweenvar,let...
You declare a JavaScript variable with thevaror theletkeyword: varcarName; or: letcarName; After the declaration, the variable has no value (technically it isundefined). Toassigna value to the variable, use the equal sign: carName ="Volvo"; ...
Declare (create) stringsDeclare (create) numbersDeclare (create) an arrayDeclare (create) an objectFind the type of a variableAdding two numbers and a stringAdding a string and two numbersAn undefined variableAn empty variable JavaScript Objects ...
a multiline comment. */ 复制 变量和赋值 在JavaScript 中,变量在使用之前被声明: varfoo;// declare variable `foo` 复制 赋值 您可以声明一个变量并同时赋值: varfoo=6; 复制 您也可以给现有变量赋值: foo=4;// change variable `foo` 复制 复合赋值运算符 有复合赋值运算符,比如+=。以下两个赋值是等...
Assuming strict mode,varwill let you re-declare the same variable in the same scope. On the other hand,letwill not: 'use strict';letme ='foo';letme ='bar';// SyntaxError: Identifier 'me' has already been declared 'use strict';varme ='foo';varme ='bar';// No problem, `me` is ...
This chapter first explains how to use variables and then goes into detail on how they work (environments, closures, etc.). Declaring a Variable In JavaScript, you declare a variable via avarstatement beforeyou use it: varfoo;foo=3;// OK, has been declaredbar=5;// not OK, an undeclar...
7.3 Never declare a function in a non-function block (if, while, etc). Assign the function to a variable instead. Browsers will allow you to do it, but they all interpret it differently, which is bad news bears. eslint: no-loop-func...
Here is an example of a query to find declaration statements that declare the same variable more than once, excluding results in minified code: import javascript from DeclStmt ds, VariableDeclarator d1, VariableDeclarator d2, Variable v, int i, int j where d1 = ds.getDecl(i) and d2 =...
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I've heard that it's described as alocalvariable, but I'm still not quite sure how it behaves differently than thevarkeyword. What are the differences?. When shouldletbe used instead ofvar? 回答1 The difference is scoping.varis scoped to the nearest function block andletis scoped to the...