为什么我们在javascript for循环中使用-1？

Question

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)); 

Answer 1

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