Default function parameters

The default function parameters in ES6, gives us the ability to initialize the function arguments with default values in case if they are undefined. For example,

function mult(a, b) {
  b = typeof b !== 'undefined' ?  b : 1;
  return a*b;
}
mult(5); // 5

function multiply(a, b = 1) {
  return a*b;
}
mult(5); // 5

Also Read:

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3. Passing arguments from one function to another in javascript
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5. The JavaScript Prototype Property - Visualized