I want to check if a function returns true for any item in an array within a function in JavaScript? I'm a mere sapling btw.

No dice unfortunately, maybe I'm not being specific enough... I want any to return true if fun identifies the array to be full and any to return false if the array is empty.

    function any(arr, fun){ 
    for (var i=0; i<arr.length; i++) {  
    if (loop(fun)=== 'false')      //<--- this is what I'm not sure about
    return false;
    if (arr.length>0);
    return true;
    } 
}

I want to check if a function returns true for any item in an array within a function in JavaScript? I'm a mere sapling btw.

No dice unfortunately, maybe I'm not being specific enough... I want any to return true if fun identifies the array to be full and any to return false if the array is empty.

    function any(arr, fun){ 
    for (var i=0; i<arr.length; i++) {  
    if (loop(fun)=== 'false')      //<--- this is what I'm not sure about
    return false;
    if (arr.length>0);
    return true;
    } 
}

• javascript

• 1 Try this: if (fun(arr[i])=== 'false') Not sure what fun returns, string or boolean! – Rayon Commented Oct 27, 2015 at 20:40
• I’m not sure what that function actually looks like, but maybe Array.prototype.every helps. – Sebastian Simon Commented Oct 27, 2015 at 20:41
• Do you want to know if it returns true for any element, or for every element? Your broken code seems to be checking for every, but the text says any. – Barmar Commented Oct 27, 2015 at 20:45
• According to your new description, seems like you just want to return a boolean that will be false if arr is empty and true if it has some value in it. In that case you just need function any (arr) { return arr.length > 0; }. No extra undefined fun function is needed. – Javier Conde Commented Oct 27, 2015 at 21:32
• I want to know if it returns true for ANY element – tu6619 Commented Oct 27, 2015 at 21:50

4 Answers 4

You have a JS array function for that, it is called some. You should use it like this:

arr.some(fun);

it will return true if fun(x) equals true for any element in arr.

You can use Array.prototype.filter() to reduce the elements based on a function returning true or false.

var func = function(item) {
    return item === 'hello';
}
document.write(!!['hello','world','foo','bar'].filter(func).length + '<br>');
document.write(!!['world','foo','bar'].filter(func).length);

You need to call the function and check it's result (not sure what loop is supposed to do but it doesn't seem to help with anything):

function any(arr, fun) {
  for (var i = 0; i < arr.length; i++) {
    if (fun(arr[i]) === false) { //assuming the function returns a boolean
      return false;
    }
  }
  return true; // if we get trough the entire array they must've all been true :)
}

You can also use Array.every:

arr.every(function(item) {
  return fun(item); 
});

I came up with this: http://jsfiddle/rbroden/k5qq4ngy/

var arr = [
    false,
    false,
    false,
    true,
    false];

function fun(arrElement){
    return arrElement;
}

function any(array){
    var bool = false;

    for(i = 0; i < array.length; i++){
        if(fun(array[i])) bool = true;
    }

    return bool;
}

alert(any(arr));

which basically

• has a placeholder for a boolean to keep track if the condition was ever met

• iterates through the array passed to the function

• if the function ever returns a true, the placeholder bool will be changed to true
• at the end of the function, return the result of the function on bool