javaScript проверяет, не определено или нулевое
if( typeof myVar === 'undefined' || myVar === null ){
// myVar is undefined or null
}
Grepper
if( typeof myVar === 'undefined' || myVar === null ){
// myVar is undefined or null
}if(typeof comment === 'undefined') {
alert('Variable "comment" is undefined.');
} else if(comment === null){
alert('Variable "comment" is null.');
}if (typeof value !== 'undefined' && value) {
//deal with value'
};var myVar=null;
if(myVar === null){
//I am null;
}
if (typeof myVar === 'undefined'){
//myVar is undefined
}
if( value ) {
}