When should I use "var", "let" and "const" in TypeScript

Question

I just start coding in TypeScript. So please excuse my newbie question.

I have this method:

public copyToDest() { for (var i = 0; i < this.source.length; i++) { var item = this.source[i]; if (item && item.isValid) this.dest.push(item); } }

Which is working fine. After installing a refactoring tool, I got 2 suggestions:

Change var i = 0; to let i = 0;
Change var item = ... to const item = ...

Is there any rule I'm missing about proper use of var, let and const? Or should I just ignore these suggestions?

Related: In TypeScript, when do you use “let” and when do you use “const”? — crashmstr
– crashmstr, Commented Sep 15, 2017 at 15:26

Craig W. · Accepted Answer · 2017-09-15 15:22:55Z

22

Use let when the variable's value can be changed.

Use const when the variable's value cannot/should not be changed.

Do not use var.

answered Sep 15, 2017 at 15:22

Craig W.

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1 Comment

John Weisz Over a year ago

@Vladimir830 -- No, but var is considered conceptually flawed by many, in that its declaration is always moved to the top of the current function scope. let was introduced to offer a more sensible alternative without breaking code that already relies on the original behavior of var.

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