access to this.var in _.filter?

Question

I hava a variable this.myvar which is a array. I would like to make a _.filter() with this variable, but within the _.filter()-function my this.myvar is not known.

is there a way to solve this, or did I comepletely misunderstood something?

this.my_array = ['aaa', 'bbb', 'ccc', 'ddd'];
this.my_filter = ['aaa', 'ccc'];

my_filtered_object = _.filter(this.my_array, function(item) {           
    alert(this.my_filter.toSource());   
    /*          
    if(this.my_filter.indexOf(item) != -1) {
                return item;
    }
    */
});

the alert should show the values of this.my_filter but it seems that there is no access within _.filter() to that variable

Possible duplicate of [How does the "this" keyword work?](http://stackoverflow.com/questions/3127429/how-does-the-this-keyword-work) — str, Aug 04 '16 at 08:12
check this answer http://stackoverflow.com/questions/21586688/callback-function-with-underscore-each#answer-21592953 — uzaif, Aug 04 '16 at 08:14

robertklep · Answer 1 · 2016-08-04T08:28:23.843

There are various solutions.

Store a reference in a separate variable:

var my_filter = this.my_filter;
my_filtered_object = _.filter(this.my_array, function(item) {           
  alert(my_filter.toSource());   
});

Set the context (this) inside _.filter() to point to the this outside the function:

my_filtered_object = _.filter(this.my_array, function(item) {           
  alert(this.my_filter.toSource());   
}, this);

Use an arrow function expression (although this might not work in every browser):

my_filtered_object = _.filter(this.my_array, item => {
  alert(this.my_filter.toSource());
});

Use _.bind(), as suggested by Mario in his answer.

Solution #2 makes most sense to me.

score 2 · Accepted Answer · answered Aug 04 '16 at 08:17

The anonymous function you pass to the _.filter() need to be bind to your context if you want to access the this.my_filter.

With underscore you just need to change your code as follow:

my_filtered_object = _.filter(this.my_array, _.bind(function(item) {           
    alert(this.my_filter.toSource());   
    /*          
    if(this.my_filter.indexOf(item) != -1) {
                return item;
    }
    */
}, this));

As you can see I added the _.bind() method that attach the context you need to the anonymous function.

access to this.var in _.filter?

2 Answers2