DRY way to check parameters in JavaScript

Question

I have two similiar functions that both require the same parameter checks

function doThis(foo, bar) {
    if (foo.length === 0) foo = 'foo';
    if (bar.length === 0) bar = 'bar';

    foo = encodeURI(foo);
    bar = encodeURI(bar);

    // ... some other checks and enforcements...

    // Output as alert
    alert(foo + bar);
}

function doThat(foo, bar) {
    if (foo.length === 0) foo = 'foo';
    if (bar.length === 0) bar = 'bar';

    foo = encodeURI(foo);
    bar = encodeURI(bar);

    // ... some other checks and enforcements...

    // Output on console
    console.log(foo + bar);
}

What is a proper way to dry this up? I came up with this:

function paramsCheck(foo, bar) {
    if (foo.length === 0) foo = 'foo';
    if (bar.length === 0) bar = 'bar';

    foo = encodeURI(foo);
    bar = encodeURI(bar);

    // maybe some other checks and enforcements...

    return { foo: foo, bar: bar };
}

function doThis(foo, bar) {
    var params = paramsCheck(foo, bar);

    // Output
    alert(params.foo + params.bar);
}

function doThat(foo, bar) {
    var params = paramsCheck(foo, bar);

    // Output
    console.log(params.foo + params.bar);
}

But I'm not really happy with it. I would rather like pass the parameters as references to paramsCheck(), so I can directly modify them instead of returning a new object.

This way is fine and there is nothing better (with the possible exception of merging all parameters in one object, in which case you can pass it to a function for massaging). — Jon
– Jon, Commented Jun 27, 2013 at 8:28
I would only suggest to extract setting default value to an util function. Gruss aus Winterthur. :) — Thomas
– Thomas, Commented Jun 27, 2013 at 8:33
@Thomas Zuberbühler: Einen festlichen Gruss zurück ;-) (Bin gerade in Zürich) — Sandro
– Sandro, Commented Jun 27, 2013 at 9:24

Niet the Dark Absol · Accepted Answer · 2013-06-27 08:28:45Z

2

That could work, although with what you've given I would suggest something like this:

function paramsCheck(params) {
    var l = params.length, i;
    for( i in params) if( params.hasOwnProperty(i)) {
        params[i] = encodeURI(params[i] === 0 ? i : params[i]);
    }
}
function doThis(foo,bar) {
    var params = {foo:foo,bar:bar};
    paramsCheck(params);
    // now do stuff
}

This solution is more flexible because it doesn't make assumptions about the input, so you can very easily add a third parameter.

answered Jun 27, 2013 at 8:28

Niet the Dark Absol

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2 Comments

Arun P Johny Over a year ago

what about the default value?

Niet the Dark Absol Over a year ago

Well, that's what the ` ? i` part is for - the keys are the default values in the examples, so I rolled with it.

Arun P Johny · Accepted Answer · 2013-06-27 08:28:15Z

1

You can do

function doThis(foo, bar) {
    foo = clean(foo, 'foo');
    bar = clean(bar, 'bar');

    // ... some other checks and enforcements...

    // Output as alert
    alert(foo + bar);
}

function clean(value, defaultValue){
    if (value.length === 0) value = defaultValue;
    return encodeURI(value);
}

answered Jun 27, 2013 at 8:28

Arun P Johny

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