Calling function in forEach with extra parameters

Question

I am trying to substitute an anonymous function call in javascript, for a real function in a forEach.

What I have is something like:

whatever: function( importantParam ) {
  array.forEach( function ( val ) {
      if ( val === importantParam ) console.log( "OK" );
  } );
}

What I want to achieve is something like:

whatever: function( importantParam ) {
  array.forEach(this.whatever2,this);
},
whatever2: function( p1, importantParam) {
      if ( p1 === importantParam ) console.log( "OK" );
}

So the problem is that I don't really know how to pass the importantParam when i call whatever2 inside forEach, since it takes a function as argument with 2 arguments for they index and the value, and nothing else.

Answer 1

You'll need to wrap whatever2 somehow, eg using .bind

var array = [1, 2, 3],
    obj;
obj = {
    whatever: function (importantParam) {
        array.forEach(this.whatever2.bind(this, importantParam));
    },
    whatever2: function (importantParam, p1) {
        if (p1 === importantParam)
            console.log("OK");
    }
};

obj.whatever(2); // logs OK

In ES6 you can clean this up and use arrow functions

let obj = {
    whatever(importantParam) {
        array.forEach(x => this.whatever2(x, importantParam));
    },
    whatever2(p1, importantParam) {
        if (p1 === importantParam)
            console.log("OK");
    }
};

---

Please note that this example use case you've provided looks like you should actually use .some instead of .forEach and return true where you do the log

Answer 2

Wrap it with another function

whatever: function( importantParam ) {
  array.forEach(function(item) {
     this.whatever2(item, importantParam);
  },this);
},

or switch the order of arguments and use bind to partially apply callback

whatever: function( importantParam ) {
  array.forEach(this.whatever2.bind(this, importantParam));
},
whatever2: function(importantParam, p1) {
      if ( p1 === importantParam ) console.log( "OK" );
}