Trouble using forEach on typecasted array

Question

I'm using Typescript ~2.4 if it matters.

I have a variable that is cast as {} | {}[] | string[]. I do a check when it's an array, and want to iterate over it. I figured a forEach is best on that:

(<{}[] | string[]>data).forEach((val) => {
    this.options.push(setupValue(val));
});

But it says Cannot invoke an expression whose type lacks a call signature. I can't see where I went wrong. I can't tell if this is a problem with how I'm using Typescript or my own logic?

Interestingly, both (<{}[]>data).forEach and (<string[]>data).forEach are fine. — cartant
– cartant, Commented Sep 25, 2017 at 4:07
So maybe it's a bug with Typescript? Or seems like intended behavior? — Rohit
– Rohit, Commented Sep 25, 2017 at 4:22
Looks buggy, to me, but others might know more about the specifics. — cartant
– cartant, Commented Sep 25, 2017 at 4:23

isp-zax · Accepted Answer · 2017-09-25 04:39:24Z

1

I think it's this issue: Can't call array methods on type (A[] | B[]) #18602

answered Sep 25, 2017 at 4:39

isp-zax

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1 Comment

Rohit Over a year ago

Thanks. Don't know how I missed that (I did check the bugs). Seems like it's something they're not going to address either...

Romain Deneau · Accepted Answer · 2017-09-25 11:28:57Z

1

You've got an array of empty objects ({}) or strings. If you accept to deal with an array of both, the TypeScript compiler lets you write :

(<({} | string)[]>data).forEach(val => {
    //...
});

answered Sep 25, 2017 at 11:28

Romain Deneau

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1 Comment

Rohit Over a year ago

Yah, this is the workaround that seems to work, though it's not an accurate representation of my typing.

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