Check if a variable is in the scope or not in Javascript

I need to check if a obje开发者_JS百科ct "objCR" is present in the current scope or not. I tried using below code.

if(objCR == null)
alert("object is not defined");

Let me know where I am wrong.

Use the typeof operator:

if(typeof objCR == "undefined")
   alert("objCR is not defined");

if (typeof objCR=="undefined"){
    alert("objCR is undefined");
} else {
    alert("objCR is defined");
};

(!objCR) will return true if objCR is a boolean equal to false

As mentioned by others, using a typeof check will get you some of the way there:

if (typeof objCR == "undefined") {
    alert("objCR is undefined");
}

However, this won't distinguish between objCR existing and being undefined (as would be the case if it had been declared but not assigned to, e.g. using var objCR;) and objCR never having been declared anywhere in the scope chain, which I think is what you actually want. If you want to be sure that no objCR variable has even been declared, you could use try/catch as follows:

try {
    objCR; // ReferenceError is thrown if objCR is undeclared
} catch (ex) {
    alert("objCR has not been declared");
}

I would suggest the obvious:

if (objCR==undefined) ...

I always have this to be safe:

if(typeof objCR == "undefined" || objCR == null)
   alert("object is not defined or null");