Javascript – Is checking for true explicity bad by design

javascriptweakly-typed

Is it considered bad to explicitly check for the boolean true. Would it be better to do a simple if(success) ?

I've seen various jokes made about how if (someBoolean === true) is horrible code in a strongly typed language but is it also considered bad in weakly typed languages?

This would apply for any weakly typed language that does type coercion on an if statement.

A specific example would be :

var onSuccess = function (JSONfromServer) {
    // explicitly check for the boolean value `true`
    if (JSONfromServer === true) {
         // do some things
    }
}

// pass it to an ajax as a callback
doSomeAjax(onSuccess);

[Edit]

In this particular case the success variable is any valid JSON returned from a server. So it could be anything. if its the boolean true then a success happened. If it's some error handling object then it will be handled. If it's something else then it will probably be handled quietly.

The question was is getting the server to return true as JSON and checking for a good way to handle the case where the action succeeded.

I wanted to avoid being specific to JavaScript & AJAX though.

Best Answer

With Javascript its worth knowing that beyond boolean true and false, values can be truthy and falsy.

Consider:

if (false)     // evaluates to false.
if (0)         // evaluates to false, 0 is falsy.
if ("")        // evaluates to false, empty strings are falsy.
if (null)      // evaluates to false, null values are falsy.
if (undefined) // evaluates to false, undefined values are falsy.
if (NaN)       // evaluates to false, NaN is falsy.

All other values for objects are truthy.

If truthy and falsy values are leading to errors in your logic, you should consider explicitly using === and !== operators to ensure objects are compared by type and value.

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In JavaScript, everything is 'truthy' or 'falsy', and for numbers 0 means false, everything else true. So you could write:

if ($(selector).length)

You don't need that >0 part.

Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

I use javascript:void(0).

Three reasons. Encouraging the use of # amongst a team of developers inevitably leads to some using the return value of the function called like this:

function doSomething() {
    //Some code
    return false;
}

But then they forget to use return doSomething() in the onclick and just use doSomething().

A second reason for avoiding # is that the final return false; will not execute if the called function throws an error. Hence the developers have to also remember to handle any error appropriately in the called function.

A third reason is that there are cases where the onclick event property is assigned dynamically. I prefer to be able to call a function or assign it dynamically without having to code the function specifically for one method of attachment or another. Hence my onclick (or on anything) in HTML markup look like this:

onclick="someFunc.call(this)"

onclick="someFunc.apply(this, arguments)"

Using javascript:void(0) avoids all of the above headaches, and I haven't found any examples of a downside.

So if you're a lone developer then you can clearly make your own choice, but if you work as a team you have to either state:

Use href="#", make sure onclick always contains return false; at the end, that any called function does not throw an error and if you attach a function dynamically to the onclick property make sure that as well as not throwing an error it returns false.

Use href="javascript:void(0)"

The second is clearly much easier to communicate.

Best Answer

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Javascript – n “exists” function for jQuery

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