How important is a neglected parameter in the world of JavaScript?

Curious about the value of an ignored parameter in JS? Imagine a function that requires 2 values as parameters, but you only provide one during the call. What happens to the other parameter? You might think it's undefined, but the code below only shows "1."

var test = function(par1, par2){
    document.write(par1.toString());
    document.write(par2.toString());
    if(typeof par2 === "undefined"){
        document.write('undefined');
    }
};

test(1);

If you tweak the code slightly like this:

var test = function(par1, par2){
    document.write(par1.toString());
    document.write(par2);
    if(par2 === undefined){
        document.write('undefined');
    }
};

test(1);

Answer №1

If a parameter is not provided, it defaults to having a value of undefined. It's important to note that even though the variable itself exists (since its name is passed to a function through the arguments list), there is no need to check if it's typeof var === 'undefined' to prevent ReferenceErrors.

In JavaScript, undefined is a unique value. Although you can't perform any methods on it (resulting in an error message saying undefined is not an object), you can still use it in calculations and function calls. For example, when using document.write, it will automatically convert the value to a String, displaying 'undefined' as the output.

Check out this demo.

Answer №2

Give this a try:

let sample = function(param1, param2){
    if(param2 === undefined){
        document.write('undefined value');
    }
};

sample(1);

View working example

You can also verify if your attributes are defined. For instance:

let sample = function(param1, param2){
    if(param1 === undefined){
        document.write('param1 is not defined');
    } else {
        document.write('param1 has a value');
    }
    if(param2 === undefined){
        document.write('param2 is not defined');
    } else {
        document.write('param2 has a value');
    }
};

sample(1);

The output will be:

param1 has a value
param2 is not defined

Check out Demo 2

Hoping this information proves useful :)

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