javascript function optional parameter default value code example

Example 1: javascript constructor default parameter

function greet(name, greeting, message = greeting + ' ' + name) {
  return [name, greeting, message]
}

greet('David', 'Hi')                     // ["David", "Hi", "Hi David"]
greet('David', 'Hi', 'Happy Birthday!')  // ["David", "Hi", "Happy Birthday!"]

Example 2: js default parameter

function read_file(file, default_param = false) {
  // Code
}

Example 3: variable defaults javascript es6

let variableToSet = checkedValue || defaultValue;