Variable Number of Arguments in TypeScript
JavaScript has always supported functions with variable number of arguments, although the syntax required some getting used to. In TypeScript and ECMAScript 6 rest parameters and spread syntax provide a more convenient alternative that also works with arrow functions.
The JavaScript Way
There is an arguments object available in every JavaScript function as a local variable. It contains the array of arguments that where passed to the function:
function varArgs() {
console.log(arguments.length);
}
To pass the array to another function accepting a variable number of arguments, the apply function can be used:
function varArgs() {
console.log.apply(console, arguments);
}
If you try to use the arguments object inside an arrow function, it won't work:
The 'arguments' object cannot be referenced in an arrow function in ES3 and ES5. Consider using a standard function expression.
Instead of using a function and manually handling this value, you can now use rest parameters and spread syntax.
The TypeScript / ECMAScript 6 Way
Rest parameters can be used to capture variable number of arguments into an array in a way similar to other C-like languages:
function varArgs(...args: string[]) {
console.log(args.length);
}
To pass the array to a function accepting a variable number of arguments, spread syntax can be used:
function varArgs(...args: string[]) {
console.log(...args);
}
This approach works just as well with arrow functions:
let varArgs = (...args: string[]) => {
console.log(...args);
};
