javascript - reader.onload callback issue with typescript -

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i building simple file upload using angular2. have following code. in code callback assigned onload. after context changes reader , not class in present. can't access other objects in overview class 

    export class overview {        change() {           var reader = new filereader();           reader.onload = this.uploadfile;           reader.readasdataurl($("input[name='image']")[0].files[0]);         }        uploadfile() {         console.log(this); //"this" refers reader obj,how can overview object        this.api('upload'); //this not work because api undefined        }    }

the keyword takes new context based on it's caller. can override default behaviur constructor class , explicitly bind context of methods.

constructor() {     (var name in this) {         if ($.isfunction(this[name])) {             this[name] = this[name].bind(this);         }     } }

this function loops through properties of class, , uses jquery check if property method. binds context of class level. note won't have effect on anonymous functions, in case can use variable keep track of this. such 

public test(): void {     var self = this;     something.callback = function() {         console.log(this);         console.log(self); //will class level     } }

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