check if value is set javascript code example

Example 1: javascript check if variable exists

if (typeof myVar !== 'undefined') {
    // myVar is defined
}

Example 2: javascript check if set

if (typeof variable !== 'undefined') {
    // the variable is defined
}
//or
if (typeof variable === 'undefined') {
    // variable is undefined
}

Example 3: check if set has value js

const mySet = new Set();

// Add value to set
mySet.add(15);

console.log(mySet.has(33)) // expected output: false
cosole.log(mySet.has(15)) // expected output: true