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why we use -1 in javascript for loop

the example code here 

var arr = [1,2,2,3,4,5,5,5,6,7,7,8,9,10,10];

function squash(arr){
    var tmp = [];
    for(var i = 0; i < arr.length; i++){
        if(tmp.indexOf(arr[i]) == -1){
        tmp.push(arr[i]);
        }
    }
    return tmp;
}

console.log(squash(arr));

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  • 2
    You use it for indexOf, not the loop. Look up the documentation on it. Commented Nov 17, 2015 at 6:38

1 Answer 1

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The indexOf function returns -1 if the item is not found in the desired array.

document.write([1, 2, 3].indexOf(1)+" "); //Exists
document.write([1, 2, 3].indexOf(0)); //Does not exist

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