JavaScript的直接量包括:字符串,数字,布尔值,对象,数组,函数,正则表达式,具有特殊意义的空值,以及未定义。 2.Variables 变量 开发人员使用var关键字创建用于存储数据值。 3.Array items 数组项 具有数字索引,存储一个JavaScript数组对象。 4.Object members 对象成员 具有字符串索引,存储一个JavaScript对象。 每一种数...
var y= new Boolean(); var cars= new Array(); var person= new Object(); 1. 2. 3. 4. 5. 5、变量的作用域: 一个变量的作用域(scope)是程序源代码中定义的变量的区域。全局变量拥有全局变量区域,在函数内部声明的变量只能在函数内有定义,是局部变量。函数参数也是局部变量,在函数体内,局部变量的优...
you can create a nested scope by defining a function. Inside such a function, you can again nest scopes. Each scope has access to its own variables and to
Tips while using the variables in JS. Literal values and local variables are faster to accessible than Array and objects. Local variables are faster to access as they are in first level of scope chain and Global are slowest as they exist in last level. ...
The JavaScript compiler invisibly moves (hoists) all the variables to the top of their containing scope. Consider this code: function f() { doSomething(); var count; } JavaScript transforms the above code to this: function f() { var count; // hoisted doSomething(); } All variables ...
Chapter 2： Variable Scope Item 8： Minimize Use of the Global Object Item 9： Always Declare Local Variables Item 10： Avoid with Item 11： Get Comfortable with Closures Item 12： Understand Variable Hoisting Item 13： Use Immediately Invoked Function Expressions to Create Loc...
“Use the array literal notation [].”:“使用数组的符号 []“, “Expected an operator and instead saw ‘{a}’.”:“需要用一个符号来代替’{a}’”, “Unexpected space after ‘{a}’.”:“在’{a}’之后不能出现空格”, “Unexpected space before ‘{a}’.”:“在’{a}’之前不能出现空...
2.4、数组(Array) ①js中,数组元素类型可以不一致。 ②js中,数组长度可以动态改变。 ③接着上述代码,typeof arr 和 arr instanceof Array 分别输出object和true。 代码语言:javascript 复制 console.log(typeof(names));//objectconsole.log(namesinstanceofArray);//trueconsole.log(""instanceofString);//false...
number is interpreted as ordinality for initializing an empty array. Boolean and string are not JavaScript objects, and can be easily represented in JavaScript variables. If the JSON copy fails, an exception is thrown. JSON Serialization Support Because of the inability to walk JavaScript ...