Can you provide a method for verifying an 'undefined' variable in AJAX queries?

How can we elegantly check if a variable is undefined in JavaScript?

$.ajax({
    type: method,
    url: url,
    success: function (data) {
        if (form != null || form != undefined){
            data = $(form).serialize();
        }
        var json =  JSON.parse(data),
            list = $(table).html(),
            compileTemplate = Handlebars.compile(list),
            result = compileTemplate(json),
            content = doc.getElementById(element);
        content.innerHTML = result;
    },
    dataType: "text"
});

I'm searching for a more refined approach to handle this validation.

Answer №1

Prioritize checking if a variable is undefined before evaluating its value to prevent errors. Use an AND operator instead of an OR.

The recommended method is to verify the type.

Update the 'if' statement as follows:

if (typeof(data) !== "undefined" && data != null) {

Answer №2

To determine whether form is neither null nor undefined, you can use the condition form != null.

$.ajax({
    type: method,
    url: url,
    success: function (data) {
        if (form != null){
            data = $(form).serialize();
        }
        var json =  JSON.parse(data),
            list = $(table).html(),
            compileTemplate = Handlebars.compile(list),
            result = compileTemplate(json),
            content = doc.getElementById(element);
        content.innerHTML = result;
    },
    dataType: "text"
});

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