Variable(变量)的名字可以由数字、字母、$或者_组成,但是不能包含空格或者以数字为首。 任务 使用var关键字来创建一个名为myName的变量。 提示 如果遇到困难了,请看下ourName的例子是怎么写的。 // 举例 var ourName; var myName; // Define myName below this line JavaScript 使用=为变量赋值 在JavaScript...
这个匿名函数的参数在执行时会通过判断exports和define是否存在,来确定当前执行环境: 当前环境为CommonJS/Node.js时,匿名函数的参数就是一个手动定义的define函数 当前环境为AMD/RequireJS时,匿名函数的参数就直接是AMD中的define函数。 如此,在保证了define方法的存在后,匿名函数内部就可以直接使用define函数来创建模块。
// bracket notationobj['name']='Simon';varname=obj['name'];// can use a variable to define a keyvaruser=prompt('what is your key?')obj[user]=prompt('what is its value?') 这两种方法在语义上也是相同的。第二种方法的优点在于属性的名称被看作一个字符串,这就意味着它可以在运行时被计算...
Object.defineProperties()方法可以定义任意数量的属性,甚至可以同时改变已有的属性并创建新属性。 var person = {}; Object.defineProperties(person, { // data property to store data _name: { value: "Nicholas", enumerable: true, configurable: true, writable: true }, // accessor property name: { g...
In browsers, the top-level scope has traditionally been the global scope. This means thatvar somethingwill define a new global variable, except within ECMAScript modules. In Node.js, this is different. The top-level scope is not the global scope;var somethinginside a Node.js module will be...
We can also assign the value to the variable at the same time as its declaration: Example: vartest =10; where var is the keyword to declare the variable, and thetestis the name of the variable, and the assigned value is10. How to define multiple variables in a single step in JavaScrip...
(2)JavaScript 引擎会为 for 循环中的 let 声明分别创建独立的变量实例,虽然 const变量跟 let 变 量很相似,但是不能用 const 来声明迭代变量(因为迭代变量会自增,自增的过程中会修改变量的值)。 4、变量声明方式的选取 (1) 不使用var 有了let 和 const,大多数开发者会发现自己不再需要 var 了。限制自己只...
DefinePlugin doesn't actually define anything. What it does is replace variables that exist in your bundle code. If the variable doesn't exist in your code, it will do nothing. So it doesn't create global variables. In order to create a global variable, write it in your code: window.My...
String（字符串）Boolean（布尔）Symbol（符号）（第六版新增）Null（空）Undefined（未定义）其余的都是...
In the example below, we have defined the variables without using the var keyword. The name variable contains the value of the string type, and the number variable contains the value of the float data type. When we define the variables without using any keyword, JavaScript considers them ...