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const callbacks = {}
/**
* 加载一个远程脚本
* @param {String} src 一个远程脚本
* @param {Function} callback 回调
*/
function loadScript(src, callback) {
const existingScript = document.getElementById(src)
const cb = callback || (() => {})
if (!existingScript) {
callbacks[src] = []
const $script = document.createElement('script')
$script.src = src
$script.id = src
$script.async = 1
document.body.appendChild($script)
const onEnd = 'onload' in $script ? stdOnEnd.bind($script) : ieOnEnd.bind($script)
onEnd($script)
}
callbacks[src].push(cb)
function stdOnEnd(script) {
script.onload = () => {
this.onerror = this.onload = null
callbacks[src].forEach(item => {
item(null, script)
})
delete callbacks[src]
}
script.onerror = () => {
this.onerror = this.onload = null
cb(new Error(`Failed to load ${src}`), script)
}
}
function ieOnEnd(script) {
script.onreadystatechange = () => {
if (this.readyState !== 'complete' && this.readyState !== 'loaded') return
this.onreadystatechange = null
callbacks[src].forEach(item => {
item(null, script)
})
delete callbacks[src]
}
}
}
/**
* 顺序加载一组远程脚本
* @param {Array} list 一组远程脚本
* @param {Function} cb 回调
*/
export function loadScriptQueue(list, cb) {
const first = list.shift()
list.length ? loadScript(first, () => loadScriptQueue(list, cb)) : loadScript(first, cb)
}
export default loadScript