I'm trying to define an interface that is an array as explained here: http://www.typescriptlang.org/Handbook#interfaces-array-types and then push items to it. The problem is that TypeScript says that push doesn't exists.
I have tried the following example in the playground:
interface StringArray {
[index: number]: string;
}
var myArray: StringArray;
myArray = ["Bob", "Fred"];
myArray.push('Barney'); // <- push doesn't exist ??
Is that interface not a regular array?
It can be just like a regular array, if you tell the compiler it is:
interface StringArray extends Array<string> {
[index: number]: string;
}
By default, your StringArray only has the members you define. There are some cases where an array-like structure doesn't support all array methods, even though it has an indexer like an array - but in your case, extending the Array interface will solve your issue.
Full example:
interface StringArray extends Array<string> {
[index: number]: string;
}
var myArray: StringArray;
myArray = ["Bob", "Fred"];
myArray.push('Barney'); // now ok
I usually don't define an interface that is an array but define an array which has the interface as type:
var myArray: string[];
myArray = ["Bob", "Fred"];
myArray.push('Barney');
I like this more because it is easier but to be honest, I don't know if there is a difference in functionallity.
There is a simple way to bypass that issue. You just use the array length property and assign the new values to the end of the array.
interface StringArray {
[index: number]: string;
}
var myArray: StringArray;
myArray = ["Bob", "Fred"];
myArray[myArray.length] = 'Barney';
