JS Strict mode

Use Strict is a feature of ECMASCRIPT5 and is not recommended to be used globally, because when you compress different files, a file uses the use strict, a file that is not used, and does not use strict will be error-free.

1. Role

Eliminate the problem that JS syntax is unreasonable, not rigorous, unsafe, improve compiler efficiency, increase running speed

2. Supported Browsers

Ie10+,firefox4+,safari12+,opera12+,chrome

3. Rules

Variable:

Create global variable eg:name = "Bella" is not allowed;

You cannot delete a variable eg:var name = "Bella"; Delete name;

Object:

Cannot assign a value to a read-only property:

ECMAscript5 appeared the Object.definepropotype method changed the JavaScript language in which all object is public;

Object.definepropotype (obj,prop,descriptor): objects that need to be added or modified, property names, property descriptions;

var person = {name: ' Bella ', Sex: ' Female '};object.definepropotype (person, ' name ', {value: ' Alias ', Writable:false})

You cannot use the delete operation for a non-configurable property

Not configurable is also set by Object.definepropotype.

var person = {name: ' Bella ', Sex: ' Female '};object.definepropotype (person, ' name ', {configurable:false})

Function:

Parameter must be unique Eg:function (a,a) {}

Modifying a parameter does not affect arguments eg:funtion (arg1) {arg1 = "Bella";} Arguments[0]:bella,arguments was modified in non-strict mode

Use of Arguments.callee and Arguments.caller is not allowed

Eval () is not allowed to create a variable or function in the containing context

Eval is rarely used, because Eval executes the string as a JS code, changing the context Eg:eval ("var x = 10"); Alert (x) This is not allowed

This is not allowed to be null or undefined

Using with statements is not allowed

Octal literals are not allowed

JS Strict mode