Javascript: use either a variable, or if it's undefined, a default string

javascript function variables undefined

hardmax · Feb 24, 2012 · Viewed 42.7k times · Source

I have this code:

var phrase = function (variable, defaultPhrase) {
    if (typeof variable === "undefined") {
        return defaultPhrase;
    }
    else {
        return variable;
    }
}

It's called like this:

Ext.Msg.show({title: phrase(js_shutdown,'Shutdown'), //...

What I want to do is to use a default phrase when the variable is not defined, but when I pass an undefined variable to phrase(), JS throws an undefined variable error. How do I fix this? Any other ideas to do this?

Answer

You don't need a function. The || operator is usually used:

Ext.Msg.show({ title: js_shutdown || 'Shutdown', //...

You can see || as:

someValue || defaultValue

For strings, defaultValue is used if someValue === "".

If the variable is not defined at all, you'll need to inline the typeof x === "undefined" check, because you cannot pass the variable to a function (that's a ReferenceError).

Javascript: use either a variable, or if it's undefined, a default string

Answer

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