Javascript减少功能不适用于此obj

Question

I am new to Javascript and trying to execute below code on parent object but it is not working as expected. Please help.

The below code doesn't work as expected and throws error as:

"TypeError: this.reduce is not a function"

Array.prototype.merge = merge = this.reduce(function(arg1,arg2)   {
    return arg1+arg2;
},[]);

var arrays =  [1,2,3,4,5,6];
console.log(arrays.merge);

It throws error as below:

TypeError: this.reduce is not a function
    at Object.<anonymous> (C:\Program Files\nodejs\merge.js:1:100)
    at Module._compile (module.js:434:26)
    at Object.Module._extensions..js (module.js:452:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:475:10)
    at startup (node.js:117:18)
    at node.js:951:3

If I call array directly, it works fine but that is not what I want to do. I should be able to pass array as shown on above example code.

Array.prototype.merge = merge = [1,2,3,4,5,6].reduce(function(arg1,arg2)   {
    return arg1+arg2;
},[]);

console.log(arrays.merge);

Answer 1

This should do the trick!

Array.prototype.merge = function () {
    return this.reduce(function (arg1, arg2) {return arg1 + arg2;},[]);
};

By the way, this works because in this case, this is the object that the method is being called on, which is your merge function.

Answer 2

Use Object.defineProperty - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty

Object.defineProperty(Array.prototype, 'merge', {
  get: function() { return this.join(''); },
  enumerable: false,
  configurable: true
});

or - using reduce

Object.defineProperty(Array.prototype, 'merge', {
  get: function() { 
    return this.reduce(function (arg1, arg2) {
      return arg1 + arg2;
     }, []); 
  },
  enumerable: false,
  configurable: true
});

This code will allow you to do what you've said in a couple of comments

console.log([1,2,3,4,5].merge);

instead of

console.log([1,2,3,4,5].merge());

Answer 3

I would add a merge function to the Array.prototype like this:

Array.prototype.merge = function () {
    return this.reduce(function (arg1, arg2) {
        return +arg1 + +arg2;
    }, []);
};


var arrays = [1, 2, 3, 4, 5, 6];
console.log(arrays.merge());

More about the this keyword in Javascript here .