default-function-parameters.md

Default function parameters

Today's TIL is short but sweet and I cannot believe I was not aware of this new ES6 feature before. So, today I found out that you can set default values in ES6, similarly to Java for example.

In the example below, we supply function multiply with only one parameter setting a to 5. Since we do not declare the second parameter, the default one is used which is 1. In the second call we do declare b to 2, and thus default value is no longer used.

function multiply(a, b = 1) {
  return a*b;
}

multiply(5); // 5
multiply(5, 2); // 10

The code above is essentially a syntactic sugar, albeit an awesome one, for ES5 function below:

function multiply(a, b) {
  var b = typeof b !== 'undefined' ?  b : 1;

  return a*b;
}

multiply(5); // 5

Resources

• Default parameters (MDN)