Angular 4打字稿：无法读取未定义的属性“列表”

Question

I'm initializing an array and trying to push elements into the array. But I get this error saying Cannot read property 'list' of undefined.

list: Array<any> = [];
this.data.forEach(function(element) {
      this.list = [];

    });
    this.data.forEach(function(element) {

        this.list.push({
          'name' : this.url
        })
  });

Even though I'm initializing the array, it is saying as undefined

Answer 1

use an arrow function to preserve the "this" context like

(element) => { } 

instead of

function(element) { } 

arrow functions don't create new scope, regular functions do, so "this" refers to the function scope (where list is undeclared) in a normal function declaration rather than the component scope (where list is declared) like you want.

generally, you will be using arrow functions much more often than not. regular function declaration is the more specialized case.