I am using Angular 2 with TypeScript 2.
When I use
let labels: string[] | number[] = [];
// let labels: Array<number> | Array<string> = [];
labels.push(1);
it gives me error:
error TS2349: Cannot invoke an expression whose type lacks a call signature.
Changing
let labels: string[] | number[] = [];
to either of these
let labels: (string | number)[] = [];
let labels: Array<number|string> = [];
will solve the issue.
string[] | number[] is equivalent to (string | number)[]. I think the first option means labels will be either an array of all strings, or an array of all numbers. While the second option means labels is an array whose contents can be strings or numbers, interchangeably. Any thoughts on that?
filter because I imagine filter uses push under the covers. It makes sense that push doesn't work because: if labels is string[] rather than number[] than this code obviously wouldn't work: labels.push(1).