werewolf. This is because instead of creating a new local variable withvar, you are reassigning the same variable in the same scope.vardoes not recognizeifto be part of a different, new scope. It is generally recommended that you declare variables that are block...
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 ...
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...
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...
defined in the global scope or what they are being used for. Thus, if a function uses a global variable instead of a local one, it runs the risk of changing a value on which some other part of the program relies. Fortunately, avoiding this problem is simple: declare all variables with...