Array definitions in TypeScript

Question

What's the difference between the following declarations:

var num1: [number];
var num2: number[];
var num3: Array<number>;

It seems that num2 and num3 are interchangeable, but what about num1?

Which declaration should I use when?

Can you make your question title do more than just name a language and a feature? With 8.69 million questions on Stack Overflow, it is helpful when titles really describe the question. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 18, 2015 at 11:23
@LightnessRacesinOrbit I am here because of google where I searched for almost the exact same string as this title and ended up here. So disagree. — Clark
– Clark, Commented Jan 19, 2015 at 10:00
@Clark: You got lucky. You're also but a single sample. The benefits of a good, unique question title are both well-documented and self-evident. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 19, 2015 at 17:46

score 4 · Accepted Answer · 2015-01-18 11:16:40Z

4

1 is a tuple type, so in this case num1 must be a 1-element array containing a number. If you declare it as var num1: [number, string, string]; then num1 must be a 3-element array containing a number, a string and another string in that order.

2 and 3 are identical; it doesn't matter which one you use.

edited Jan 18, 2015 at 11:16

answered Jan 18, 2015 at 11:03

user1804599

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1 Comment

Clark Over a year ago

Compare the dry pages of documentation to the first 2 lines of this answer. I came here to see the difference between [] and <> for arrays, and ended up understanding tuple types. Awesome.

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