TypeScript Variable Undefined inside array.forEach()

Question

I will try to explain my problem. I have an array of a particular object and, from this array, I want to create a new one with the value of a particular field of each object.

In order to achieve this, I tried to use array.forEach() method but I get a variable undefined error inside the forEach() function. This is my code:

var values: number[];
measures.forEach((measure)=>{
    values.push(measure.value);
});

I've tried to declare the array values as public (and access this.values) and also to declare it in the function where I make the forEach and neither way worked.

Here is the error I get in the browser (angular CLI reports no problem):

ERROR TypeError: "values is undefined"

You must initialize the array: let values: number[] = [];. — Martin Parenteau
– Martin Parenteau, Commented Apr 3, 2019 at 19:27
You need to initialize the values array, not just define. Try values: number[] = []; instead. — Krishna Veeramachaneni
– Krishna Veeramachaneni, Commented Apr 3, 2019 at 19:27

Saksham · Accepted Answer · 2019-04-03 19:39:25Z

2

Try to initialize your array rather than just declare it as

values: number[] = [];

You do not need the var keyword in angular if you are declaring a variable directly inside a component class. If you need to do it inside a function, use let keyword. more information HERE

edited Apr 3, 2019 at 19:39

answered Apr 3, 2019 at 19:30

Saksham

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2 Comments

nlopez Over a year ago

I do need the var keyword If I create my array inside a function.

Saksham Over a year ago

then use let, not var @nlopez

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