Default Params

Old ES5 way to set default params

Approach 1: easy way.

// This is what people normally do in ES5 to set default params
function link(height, color, callbackFn) {
  var height = height || 50;
  var color = color || 'red';
  var callbackFn = callbackFn || function() {};

  // function content...
}

It works well, but in the above implementation we didn't account for falsy values. For example: 0, '', null, NaN, false are falsy values.

Approach 2: Better way.

// So there is a better way to do this, it checks param is actually undefined or not:
function link(height, color, callbackFn) {
  var height = typeof height !== 'undefined' ?  height : 50;
  var color = typeof color !== 'undefined' ?  color : 'red';
  var callbackFn = typeof callbackFn !== 'undefined' ?  callbackFn : function() {};

  // function content...
}

ES6 way to write default params

Approach 3: ES6 way, it gets just so much better.

function link(height = 50, color = 'red', callbackFn = () => {}) {
  // function content...
}

// or using ES6 const and let
const noop = () => {};
const link = (height = 50, color = 'red', callbackFn = noop) => {
  // function content...
};

Further reading:

• https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/default_parameters

• http://tc39wiki.calculist.org/es6/default-parameter-values/

• http://exploringjs.com/es6/ch_parameter-handling.html

• https://dorey.github.io/JavaScript-Equality-Table