How to check if a parameter has been passed

Question

I'm passing parameters to a function in a JavaScript library I wrote:

ffff.setup({
    'size':{'width':'100','height':'100'}
});

In the function, I pick them up:

var ffff = {
    setup: function(config) {
        if (config["size"]["width"]) {my_width = config["size"]["width"];}
        if (config["size"]["height"]) {my_height = config["size"]["height"];}
    }
}

My error is, if I do not specify a parameter, I get a Cannot read property 'height' of undefined error: (the error occurs on if (config["size"]["height"]))

ffffr.setup({
    'size':{'width':'100'}
});

How should I detect if a variable has been provided or not?

possible duplicate of [How can I check whether a variable is defined in JavaScript?](http://stackoverflow.com/questions/519145/how-can-i-check-whether-a-variable-is-defined-in-javascript) — Evan Davis, Jan 02 '14 at 18:32
Why do you need to assign them to local variables? You can just use the object. Also, are those supposed to be globals? Because you didn't declare them... — elclanrs, Jan 02 '14 at 18:33
6+ answers and none suggest a mixin approach for setting defaults. I'm disappoint. — Fabrício Matté, Jan 02 '14 at 18:34
@Barmar 'file' was a variable I used in my full code. Here it should read 'height' — Patrick Keane, Jan 02 '14 at 18:36
I'd recommend checking [this approach](http://stackoverflow.com/q/7124960/1331430), just replace the `$.extend` with a deep extend algorithm. — Fabrício Matté, Jan 02 '14 at 18:47

score 4 · Answer 1 · answered Jan 02 '14 at 18:32

4

There may be more elegant approaches to this (such as jQuery extends() if you use that library), but at a very basic level you could just do

if(typeof config['size'] !== "undefined" && typeof config['size']['height'] !== "undefined")

answered Jan 02 '14 at 18:32

Lee

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1

There's really no point on doing the `typeof` check as the object surely exists, you could simply use the `in` operator like: `if ('size' in config && 'height' in config.size)` – elclanrs Jan 02 '14 at 18:36
@elclanrs seems to have the nicest fix. – Patrick Keane Jan 02 '14 at 18:52

score 1 · Answer 2 · answered Jan 02 '14 at 18:33

1

If you are looking at the config object, you can use .hasOwnProperty^MDN

if( config.hasOwnProperty("propName") ){
 //use config.propName
}

answered Jan 02 '14 at 18:33

Travis J

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score 1 · Answer 3 · answered Jan 02 '14 at 18:33

1

if (config.size && config.size.width) ...

answered Jan 02 '14 at 18:33

lviggiani

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or as @elclanrs said above: if ('size' in config && 'height' in config.size) – Patrick Keane Jan 02 '14 at 18:51

score 0 · Answer 4 · answered Jan 02 '14 at 18:32

0

Try:

if (typeof variable === 'undefined') {
    // variable is undefined
}

Or:

if (typeof (conf) === 'object') {
    // object is undefined
}

answered Jan 02 '14 at 18:32

ajtrichards

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score 0 · Answer 5 · answered Jan 02 '14 at 18:33

0

You could use

config["size"].hasOwnProperty('width')

answered Jan 02 '14 at 18:33

ArturSkowronski

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score 0 · Answer 6 · answered Jan 02 '14 at 18:33

0

Check if it is defined, and use a ternary operator to set a default

(param===undefined)?default_value:param;

what that will do is check if it is defined, and set it to whatever you want it to if it is undefined, but keep it the same otherwise

answered Jan 02 '14 at 18:33

scrblnrd3

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How to check if a parameter has been passed

6 Answers6