Cannot read property 'push' of undefined array

Question

I am trying to populate an array with numbers starting from 2016, ending at current year.

My method looks like this

  generateYears () {
    const currentDate = new Date();
    let y = 2016;
    console.log(currentDate.getFullYear());
    for (y = 2016; y <= currentDate.getFullYear(); y++) {
        this.testYears.push(y);
    }
    console.log(this.testYears);
  }

and testYears was declared with

  testYears: number[];

I have tried to declare it any[] but got same error.

What should I do?

Do you get this error in compile-time or in runtime?

Cerberus
– Cerberus

2018-07-25 06:07:50 +00:00
Commented Jul 25, 2018 at 6:07 — Cerberus
– Cerberus, Commented Jul 25, 2018 at 6:07

EmandM · Accepted Answer · 2018-07-25 06:10:21Z

4

The number[] syntax simply sets the type of the variable, not the value. Typescript types are removed before runtime. When your code is run, testYears has never been defined with an actual value and so is undefined.

To fix, simply define testYears as

public testYears: number[] = [];

This way, testYears has both a type (number[]) and a value ([])

answered Jul 25, 2018 at 6:10

EmandM

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