How to set default parameter value in JavaScript functions ?

In general all the JavaScript functions have a default value of undefined but we can overwrite it by specifying a particular value. This prevents breaking of the code in case of missing inputs.

Let us first take a look at a problem and then we'll take a look at how default values for function parameters address that problem. Let's first create a simple function. 

let multiplyIt = function (num1, num2) {
    // So we are returning num1 times num2
    return (num1 * num2);
};

console.log(multiplyIt());

Output: This example will not throw an error but will execute. As no default value is passed it will consider the values as undefined

NaN 

Now we will assign the default values to the variables in its definition only. If no value is passed to the function will assign the newly defined default values and use that value when function is executed.

Example 1: In this example, no value is passed but the default values are changed.

//These values will only be taken if a value is not passed in
let multiplyIt = function (num1 = 2, num2 = 5) {
    return (num1 * num2);
};
console.log(multiplyIt());

Output: As no value is passed default values are taken and the function produces result based on the default value.

10

Example 2: In this example, only one value is passed so default value is used for second parameter

//In this case, these values will not be considered
let multiplyIt = function (num1 = 2, num2 = 5) {
    return (num1 * num2);
};
console.log(multiplyIt(10));

Output:

50