javascript check undefined or null

if( typeof myVar === 'undefined' || myVar === null ){
    // myVar is undefined or null
}Undefined  used for unintentionally missing values.

Null       used for intentionally missing values. if (variable === null) { //Executes only if variable is null but not undefined
  //Code here
}

if (variable == null) { //Executes if variable is null OR undefined
  //Code here
}var myVar=null;

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

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

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

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