JAVASCRIPT

javascript check if undefined or null

if( typeof myVar === 'undefined' || myVar === null ){
    // myVar is undefined or null
}

javascript syntax for check null or undefined or empty

if (typeof value !== 'undefined' && value) {
    //deal with value'
};

javascript validate if string null undefined empty

/**
  * Checks the string if undefined, null, not typeof string, empty or space(s)
  * @param {any} str string to be evaluated
  * @returns {boolean} the evaluated result
*/
function isStringNullOrWhiteSpace(str) {
    return str === undefined || str === null
                             || typeof str !== 'string'
                             || str.match(/^ *$/) !== null;
}

javascript check if undefined or null or empty string

// simple check do the job
if (myString) {
 // comes here either myString is not null,
 // or myString is not undefined,
 // or myString is not '' (empty).
}

check null or undefined in javascript

//check for null or undefined with nullish coalescing operator
let value = null ?? "Oops.. null or undefined";

console.log(value) //Oops.. null or undefined

value = 25 ?? "Oops.. null or undefined";

console.log(value) // 25

value = "" ?? "Oops.. null or undefined";

console.log(value) // ""

javascript check undefined or null

var myVar=null;

if(myVar === null){
    //I am null;
}

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

javascript check if undefined or null

// simple check do the job
if (myVar) {
 // comes here either myVar is not null,
 // or myVar is not undefined,
 // or myVar is not '' (empty string).
}

javascript check if Empty string, undefined, null

Use for Empty string, undefined, null, ...
//To check for a truthy value:

if (strValue) {
    // strValue was non-empty string, true, 42, Infinity, [], ...
}

//To check for a falsy value:
if (!strValue) {
    // strValue was empty string, false, 0, null, undefined, ...
}