CODEWITHSUNDEEP
javascriptif-statementoperator-keyword
Thelma Eckman
Thelma Eckman

Reputation: 53

Javascript if statement and && operator difference

what's the difference between this 2 code?

ONE: if xmlhttp.readystate==4, then if xmlHttp.status==200, then execute code

function handleServerResponse(){
   if(xmlHttp.readyState==4){
            if(xmlHttp.status==200){
               xmlResponse = xmlHttp.responseXML;
               xmlDocumentElement = xmlResponse.documentElement;
               message = xmlDocumentElement.firstChild.data;
               document.getElementById('underInput').innerHTML = message;
               setTimeout('process()', 1000);
         }else{
            alert('Something went wrong!');
            }
      }
}

TWO: if xmlHttp.readtState==4 and xmlHttp.Status==200 then execute code

function handleSxerverResponse(){
if(xmlHttp.readyState==4 && xmlHttp.status==200){
    xmlResponse = xmlHttp.responseXML;
    xmlDocumentElement = xmlResponse.documnetElement;
    message = xmlDocumentElement.firstChild.data;
    document.getElementById('underInput').innerHTML = message;
    setTimeout('process()', 1000);
}else{
    alert('Something went wrong!');
}

}

They both look same to me, but only the first one did what I want, instead the second one keep showing the alert message.

Upvotes: 1

Views: 132

Answers (3)

Smern
Smern

Reputation: 19066

The only difference is that in the first one, if readyState is not 4, you wont see the alert.

If you converted the first one to this:

function handleServerResponse() {
    if (xmlHttp.readyState == 4) {
        if (xmlHttp.status == 200) {
            xmlResponse = xmlHttp.responseXML;
            xmlDocumentElement = xmlResponse.documentElement;
            message = xmlDocumentElement.firstChild.data;
            document.getElementById('underInput').innerHTML = message;
            setTimeout('process()', 1000);
        } else {
            alert('Something went wrong!');
        }
    } else {
        alert('Something went wrong!'); //added this
    }
}

They would functionally be the same thing. So with the first one you could easily customize the alert based on what 'went wrong' if you wanted.

Upvotes: 0

Kevin DeVoe
Kevin DeVoe

Reputation: 602

Suppose the first part is false.

In the case of then if you will never enter the block, so you will never see the alert in the second if statement. If you use && you will enter the else block if either is false.

Upvotes: 0

Denys Séguret
Denys Séguret

Reputation: 382150

Before the ready state is 4, it is 3. And then

  • in the first case the outside test prevents the alert

  • in the second case, the else clause applies so the alert is executed.

Upvotes: 1

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