How to access variable in prototype

Question

How can i pass the context of

   Test = function(){
    this.x = //(1) How to access this in the return ?

    this.line = d3.svg.line()
        .interpolate("linear")
        .x(function (d) {
            return this.x(d.x);
        })

 }

this.x in the return will give context not as in (1) How can i access 1 in the return ?

Answer 1

You have to bind the function with the current object, with Function.prototype.bind , like this

this.line = d3.svg.line()
    .interpolate("linear")
    .x(function (d) {
        return this.x(d.x);
    }.bind(this))

Since the anonymous function is bound to the current object this , inside the function, this refer to the actual this bound.

The other common way is to retain the this object, like this

Test = function() {
    var that = this;               // Retain the value of `this`
    this.x = 1;

    this.line = d3.svg.line()
        .interpolate("linear")
        .x(function(d) {
            return that.x(d.x);    // Use `that`, instead of `this`
        })
}