如何获取数组中项的索引？

Question

var fruits = [ 'apple', 'banana', 'orange' ];

how do I find what index of the value "banana" is? (which, of course, is "1").

thanks

Answer 1

As shown here: https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf

if (!Array.prototype.indexOf)
{
  Array.prototype.indexOf = function(elt /*, from*/)
  {
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0)
         ? Math.ceil(from)
         : Math.floor(from);
    if (from < 0)
      from += len;

    for (; from < len; from++)
    {
      if (from in this &&
          this[from] === elt)
        return from;
    }
    return -1;
  };
}

Usage:

var fruits = [ 'apple', 'banana', 'orange' ];
var index = fruits.indexOf('banana');

Will return '1'

Answer 2

There is no built-in property to return the index of a particular item. If you need a function then you can use the prototype function as defined by durilai. But if you just need to find the index you can use this simple code block to return the value:

for (var i=0; i<fruits.length; i++)
{
  if (fruits[i] == "banana")
  {
    alert(i);
  }
}