When it comes to JavaScript, the evaluation order of arguments and delayed evaluation play a crucial

Question

When it comes to JavaScript, the evaluation order of arguments and delayed evaluation play a crucial

Assuming function( arg1, arg2 ), is it true that arg1 will always evaluate before arg2 (unlike traditional C)?
Is there a way to create a function where arguments are not evaluated immediately, but only on demand? For instance, in if( cond1 || cond2 ), cond2 is evaluated only if cond1 is false. Is it feasible to build a custom if-like function for this purpose?

For example, could a function similar to oracle's nvl( arg1, arg2, ... ) be devised to return the first non-null argument by lazily evaluating them? In typical function calls, all arguments are evaluated prior to executing the function body.

javascript

Answer 1

Answer №1

Function parameters are assessed before being transferred to the function, so achieving what you're requesting is not technically feasible. However, there's a workaround:

function evaluate() {
    for (var j = 0; j < arguments.length; j++) {
        var result = arguments[j]();
        if (result)
            return result;
    }
}

evaluate(function() { return true; }, 
    function() { return "hello"; }, 
    function() { return false; });

The execution of evaluate will yield the string "hello".

All function wrappers are constructed, but only the content of the first two functions are assessed within evaluate.

While this may not be the most elegant solution, it does provide a way to avoid running a costly operation in any functions following the one that returns a truthy value.

Answer 2

Function parameters are assessed before being transferred to the function, so achieving what you're requesting is not technically feasible. However, there's a workaround:

function evaluate() {
    for (var j = 0; j < arguments.length; j++) {
        var result = arguments[j]();
        if (result)
            return result;
    }
}

evaluate(function() { return true; }, 
    function() { return "hello"; }, 
    function() { return false; });

The execution of evaluate will yield the string "hello".

All function wrappers are constructed, but only the content of the first two functions are assessed within evaluate.

While this may not be the most elegant solution, it does provide a way to avoid running a costly operation in any functions following the one that returns a truthy value.

Answer 3

Answer №2

When looking at your initial example, it is important to note that if you are calling a function, the evaluations will occur in order.

However, in the second scenario, JavaScript does not evaluate every parameter (similar to C), as shown here:

if(true || x++){

In this case, x++ will never be executed.

Could you provide more details on what you are attempting to achieve?

Answer 4

When looking at your initial example, it is important to note that if you are calling a function, the evaluations will occur in order.

However, in the second scenario, JavaScript does not evaluate every parameter (similar to C), as shown here:

if(true || x++){

In this case, x++ will never be executed.

Could you provide more details on what you are attempting to achieve?

Answer 5

Answer №3

Indeed
Absolutely, when using the condition if(cond1 || cond2), cond2 is only evaluated if cond1 is false.

Check out this function that retrieves the first truthy argument:

function getFirstTruthyArgument(){
    for(var i in arguments){
        if(arguments[i]){
           return arguments[i];
        }
     }
 }

For instance,

getFirstTruthyArgument(0, null, undefined, "", "hello", "goodbye")

would output "hello".

If your goal is to obtain the first non-null argument rather than just the first truthy one, you can switch if(arguments[i]) with if(arguments[i] !== null). In this case, the function would result in 0 based on the previous example.

Answer 6

Indeed
Absolutely, when using the condition if(cond1 || cond2), cond2 is only evaluated if cond1 is false.

Check out this function that retrieves the first truthy argument:

function getFirstTruthyArgument(){
    for(var i in arguments){
        if(arguments[i]){
           return arguments[i];
        }
     }
 }

For instance,

getFirstTruthyArgument(0, null, undefined, "", "hello", "goodbye")

would output "hello".

If your goal is to obtain the first non-null argument rather than just the first truthy one, you can switch if(arguments[i]) with if(arguments[i] !== null). In this case, the function would result in 0 based on the previous example.

When it comes to JavaScript, the evaluation order of arguments and delayed evaluation play a crucial

Answer №1

Answer №2

Answer №3

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