Preset in Javascript function parameters

Question

Is it possible to make parameter presets in Javascript functions? Something like:

function teste(oi = "ola", type = 1) {

To predefine variables if they are not defined?

Answer 1

This is usually called default Parameters. And Javascript does not allow this syntax. The best that can be done is to set values early in the function:

function teste(oi, type) {
    oi = (typeof(oi) === "undefined" || oi === null) ? "ola" : oi;
    type = (typeof(type) === "undefined" || oi === null) ? 1 : type;
    //continua a função aqui
}

I put in the Github for future reference.

If you are going to use this a lot it is possible to create a function to simplify this syntax. Something like this:

function def(variable, value) {
    return (typeof(variable) === "undefined" || === null) ? value : variable;
}

Then I’d wear it like this:

function teste(oi, type) {
    oi = def(oi, "ola");
    type = def(type, 1);
    //continua a função aqui

There is an experimental way to have a syntax in the conforming language MDN documentation. This way could use the way you want. At the moment only works in Firefox.

Answer 2

There are several ways to do this, one of them is the following:

function foo(a, b)
{
   a = typeof a !== 'undefined' ? a : 'seu_valor_default_a';
   b = typeof b !== 'undefined' ? b : 'seu_valor_default_b';

   //Seu código
}

OBS.: Response copied from the original made by Tom Ritter in: https://stackoverflow.com/questions/894860/set-a-default-parameter-value-for-a-javascript-function