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RESEARCH: Posting a file with XMLHttpRequest

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二04 | 时间 2018 | 作者 红领巾 ] 0人收藏点击收藏
RESEARCH: Posting a file with XMLHttpRequest Time-stamp: <2018-11-06 14:26:38 tamara> published date: [2018-11-06 Tue 13:46] keywords: XMLHttpRequest, file upload, javascript, research, React

See: Using nothing but XMLHttpRequest < maybe not

See: Using FormData objects < necessary for files, I think

In contrast to Posting with Fetch API , this is a bit lower on the food chain in terms of JS stuff, but it lets you get access to progress events, for doing such things as displaying a progress bar. Yay.

Using FormData

MDN makes a special note:

Note: As we said, FormData objects are not stringifiable objects. If you want to stringify a submitted data, use the previous pure-AJAX example. Note also that, although in this example there are some file <input> fields, when you submit a form through the FormData API you do not need to use the FileReader API also: files are automatically loaded and uploaded. Using Event Handlers

From the top of the page, just using / setting event handlers:

function reqListener () { console.log(this.responseText); } var oReq = new XMLHttpRequest(); // this sets the 'load' event handler, which fires when the file is fully loaded. // I think this works for POST/PUT as well... oReq.addEventListener("load", reqListener); oReq.open("GET", "http://www.example.org/example.txt"); oReq.send();

There’s a note somewhere on the page saying something about progress event handlers needing to be set before the .open call.

This would load up all the event handlers for XMLHttpRequest:

let oReq = new XMLHttpRequest(); oReq.addEventListener("progress", updateProgress); oReq.addEventListener("load", transferComplete); oReq.addEventListener("error", transferFailed); oReq.addEventListener("abort", transferCanceled); oReq.open(); Progress Indication

The progress event handler takes in the progress event, which is defined at WhatWG Progress Event specification . It has 3 attributes:

lengthComputable loaded total

So progress can be calculated by:

handleProgress = event => { let progress = 0 if (event.total !== 0) { progress = event.loaded / event.total } const percentCompleted = progress * 100 this,setState({ progress, percentCompleted }) } handleLoaded = event => { this.setState({ progress: 1, percentCompleted: 100, loaded: true }) } // ... request = () => { const req = new XMLHttpRequest() req.addEventListener('progress', this.handleProgress) req.addEventListener('load', this.handleLoaded) // ... etc }

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