javaScript function - why my default argument fails?

Question

My Javascript function leads my console to return me :

TypeError: style is null

Here the snippet:

Answer 1

Default parameters is assigned only if no value or undefined is passed

let defaultStyle = {  one: 1, two: 2, three: 3 }

function styling(style = defaultStyle, ...ruleSetStock) {
  return ruleSetStock.map(ruleSet => {
    return style[ruleSet]
  })
}

console.log(styling(undefined, "one", "two", "three"))

What if i want to use default value on all sorts of falsy values such as false, '', null ?

You can't use default parameter for that but you can use ||

let style1 = {  one: 1, two: 2, three: 3 }

function styling(style, ...ruleSetStock) {
  style = style || style1
  return ruleSetStock.map(ruleSet => {
    return style[ruleSet]
  })
}

console.log(styling(undefined, "one", "two", "three"))
console.log(styling(null, "one", "two", "three"))
console.log(styling('', "one", "two", "three"))
console.log(styling(0, "one", "two", "three"))