TypeScript interface for object with arbitrary numeric property names?

Question

I have an object where all the keys are numbers and all the values are strings, like this:

var object = {
    1: "whatever",
    7: "whateverrr",
    ...
};

Is there any way I can write a TypeScript interface for this? I don't know what all the keys will be, but I do know that they will be numbers and that the values will be strings so I feel like it should be possible to do some kind of type checking.

Ryan Cavanaugh · Accepted Answer · 2014-03-11 00:29:36Z

16

You can use an index signature to represent this:

interface NumberToString {
    [n: number]: string;
}

var x: NumberToString;
x = { 1: 42 }; // Error
x[1].charAt(0); // OK

x['foo'] = 'bar'; // Still not an error, though

answered Mar 11, 2014 at 0:29

Ryan Cavanaugh

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3 Comments

dumbmatter Over a year ago

Thanks! But why does it allow x['foo'] = 'bar';?

Ryan Cavanaugh Over a year ago

Long story, but basically because x[1] === x['1'], and x['hasOwnProperty'] is still valid

WiredPrairie Over a year ago

@Jeremy -Might want to read this Q & A: stackoverflow.com/questions/21960916/…

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