javascript 属性值的json索引
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json index of property value
提问by mcgrailm
I need to get the index of the json object in an array whose by the objects id
我需要在一个数组中获取 json 对象的索引，其由对象 id
here is the example code
这是示例代码
var list = [ { _id: '4dd822c5e8a6c42aa70000ad',
metadata:
{ album: 'American IV: Man Comes Around',
song: 'Hurt',
coverart: 'http://images.mndigital.com/albums/044/585/435/m.jpeg',
artist: 'Johnny Cash',
length: 216,
mnid: '44585439' } },
{ _id: '4dd80b16e8a6c428a900007d',
metadata:
{ album: 'OK Computer (Collector\'s Edition)',
song: 'Paranoid Android',
coverart: 'http://images.mndigital.com/albums/026/832/735/m.jpeg',
artist: 'Radiohead',
length: 383,
mnid: '26832739' } },
{ _id: '4dd68694e8a6c42c80000479',
metadata:
{ album: 'The Presidents Of The United States Of America: Ten Year Super Bonus Special Anniversary Edition',
song: 'Lump',
coverart: 'http://images.mndigital.com/albums/011/698/433/m.jpeg',
artist: 'The Presidents Of The United States Of America',
length: 134,
mnid: '11698479' } }
]
then pseudo code
然后是伪代码
var index_of = list.indexOf("4dd80b16e8a6c428a900007d");
obviously that is not gonna work but I wonder if there is anyway to do this without looping to find the index ?
显然这行不通，但我想知道是否有办法在不循环查找索引的情况下执行此操作？
回答by
var i = list.length;
while( i-- ) {
if( list[i]._id === '4dd80b16e8a6c428a900007d' ) break;
}
alert(i); // will be -1 if no match was found
回答by German Attanasio
You can try Array.prototype.map, based on your example it will be:
您可以尝试Array.prototype.map，根据您的示例，它将是：
var index = list.map(function(e) { return e._id; }).indexOf('4dd822c5e8a6c42aa70000ad');
Array.prototype.mapis not available on IE7 or IE8. ES5 Compatibility
Array.prototype.map在 IE7 或 IE8 上不可用。ES5 兼容性
回答by jfriend00
Since there is no index of your data structure by _id, something is going to have to loop over the structure and find an _idvalue that matches.
由于没有数据结构的索引 by _id，因此必须遍历结构并找到_id匹配的值。
function findId(data, id) {
for (var i = 0; i < data.length; i++) {
if (data[i]._id == id) {
return(data[i]);
}
}
}
回答by Peter Olson
Just loop through the list until you find the matching id.
只需遍历列表，直到找到匹配的 id。
function indexOf(list, id) {
for (var i = 0; i < list.length; i++) {
if (list[i]._id === id) { return i; }
}
return -1;
}
回答by rlemon
function index_of(haystack, needle) {
for (var i = 0, l = haystack.length; i < l; ++i) {
if( haystack[i]._id === needle ) {
return i;
}
}
return -1;
}
console.log(index_of(list, '4dd80b16e8a6c428a900007d'));
same as the above, but caches the length of the haystack.
与上面相同，但缓存了干草堆的长度。
回答by Patrik Wallin
a prototypical way
一种典型的方式
(function(){
if (!Array.prototype.indexOfPropertyValue){
Array.prototype.indexOfPropertyValue = function(prop,value){
for (var index = 0; index < this.length; index++){
if (prop in this[index]){
if (this[index][prop] == value){
return index;
}
}
}
return -1;
}
}
})();
// usage:
list.indexOfPropertyValue('_id','4dd80b16e8a6c428a900007d'); // returns 1 (index of array);
list.indexOfPropertyValue('_id','Invalid id') // returns -1 (no result);
var indexOfArray = list.indexOfPropertyValue('_id','4dd80b16e8a6c428a900007d');
list[indexOfArray] // returns desired object.
