xmlHttp.open的第三個參數true與false

原創 平常心lzt 2020-02-24 16:42

最近的項目中有個問題，用ajax調用後臺取值，然後傳回前臺的時候，傳遞的值就沒了

後臺調試是沒有問題，最後發現問題出在xmlHttp.open()的第三個參數上


xmlHttp.open("post",url,true)

第三個參數爲true，表示JavaScript異步執行，不等待後臺返回

而爲false的時候，表示同步執行，等待返回後再執行下一步


所以，這裏如果選擇true，那異步執行的話後臺沒有返回就執行下面的輸出，當然沒有值了

換作false就好了


注：AJAX即“Asynchronous Javascript And XML”，即異步JavaScript和XML，就是這裏的異步啦

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