array.sort(compare function)

var KWs = ['1080', 'smg', 'MU', 'MEGAUPLOAD', 'MULTIUPLOAD', 'xuite', 'FB', 'FileBase', '多免空', 'JDOWNLOADER', '台版', '三區'];
function descStrLen(a, b) {
    if (a.length < b.length) return 1;
}
KWs.sort(descStrLen);

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Random Array Sort
Sorting a JavaScript array using array.sort()
螞蟻的 JavaScript: Array:變動方法
sort - MDC