Javascript - Function Function length

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Introduction

Javascript functions are objects and have properties and methods.

Each function has two properties: length and prototype.

The length property indicates the number of named arguments that the function expects: 

function sayName(name){
   console.log(name);
}

function sum(num1, num2){
   return num1 + num2;
}

function displayMessage(){
       console.log("hi");
}

console.log(sayName.length);  //1
console.log(sum.length);      //2
console.log(displayMessage.length);    //0

This code defines three functions, each with a different number of named arguments.

The sayName() function specifies one argument, so its length property is set to 1.

The sum() function specifies two arguments, so its length property is 2, and displayMessage() has no named arguments, so its length is 0.