use strict not allow use of this in node.js

2018-07-04 01:52:49

使用后“使用严格”语句在我的JS文件不允许我之后IST级使用JavaScript 这个

'use strict'

module.exports = {
  a: function() {
    var self = this //works fine upto this level
    var name = 'atul';
    function b() {
      this.name = name; //gives me error as can not set property name of undefined
    }
  }
}

this and Javascript:

this references to the global object by default. ("window" on browsers)

this references to the calling object example:

var x = {name: "x", alphabet: function(){return this;}};
x.alphabet(); // in this line, x is the calling object

this will show you the object itself.

So when you do:

...
a: function() {
  var self = this //works fine upto this level
  var name = 'atul';
  function b() {
    this.name = name; //use strict is trying to tell you something
  }// you won't have a calling object for this function.
}
...

use-strict says: this function is not even an object property or method . Since it's not a method it's this will point to the global object and lead to error prone development.

If you wish to use your code in this particular way.

module.exports = {
  a: {
       name: 'atul';
       b: function (name) {
         this.name = name; // now you have a as the property which can be called by an object a.
         //To be used as OBJECT.a.b();
    }
  };
};

this is undefined as it is not autoboxed to an object in strict mode.

First, the value passed as this to a function in strict mode is not forced into being an object (aka "boxed"). For a normal function, this is always an object: either the provided object if called with an object-valued this; the value, boxed, if called with a Boolean, string, or number this; or the global object if called with an undefined or null this. (Use call, apply, or bind to specify a particular this.) Not only is automatic boxing a performance cost, but exposing the global object in browsers is a security hazard, because the global object provides access to functionality that "secure" JavaScript environments must restrict. Thus for a strict mode function, the specified this is not boxed into an object, and if unspecified, this will be undefined