js undefined value code example

Example 1: javascript check for undefined

if (typeof myVariable === 'undefined'){
    //myVariable is undefined
}

Example 2: js this returns undefined

function foo() {
    console.log(this);
}

// normal function call
foo(); // `this` will refer to `window`

// as object method
var obj = {bar: foo};
obj.bar(); // `this` will refer to `obj`

// as constructor function
new foo(); // `this` will refer to an object that inherits from `foo.prototype`

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