learnyounode

<!doctype html>  <html lang="en"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <title></title> <meta name="description" content=""> <meta name="viewport" content="width=device-width, initial-scale=1"> <meta name="created-with" content="https://github.com/rvagg/gfm2html"> <style type="text/css"> /* most of normalize.css */ article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section,summary{display:block;}[hidden],template{display:none;}html{font-family:sans-serif;/*1*/-ms-text-size-adjust:100%;/*2*/-webkit-text-size-adjust:100%;/*2*/}body{margin:0;}a{background:transparent;}a:focus{outline:thindotted;}a:active,a:hover{outline:0;}h1{font-size:2em;margin:0.67em0;}abbr[title]{border-bottom:1pxdotted;}b,strong{font-weight:bold;}dfn{font-style:italic;}hr{-moz-box-sizing:content-box;box-sizing:content-box;height:0;}mark{background:#ff0;color:#000;}code,kbd,pre,samp{font-family:monospace,serif;font-size:1em;}pre{white-space:pre-wrap;}q{quotes:"\201C""\201D""\2018""\2019";}small{font-size:80%;}sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline;}sup{top:-0.5em;}sub{bottom:-0.25em;}img{border:0;}svg:not(:root){overflow:hidden;}table{border-collapse:collapse;border-spacing:0;} html { font: 14px 'Helvetica Neue', Helvetica, arial, freesans, clean, sans-serif; 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For when through2 is just too verbose :wink: Note you will NOT be able to skip chunks. This is intended for modification only. If you want filter the stream content, use either <code>through2</code> or <code>through2-filter</code>. IMPORTANT: If you return <code>null</code> from your function, the stream will end there. <div class="highlight"><pre>var map = require("through2-map") var truncate = map(function (chunk) { return chunk.slice(0, 10) }) // vs. with through2: var truncate = through2(function (chunk, encoding, callback) { this.push(chunk.slice(0, 10)) return callback() }) // Then use your map: source.pipe(truncate).pipe(sink) // Additionally accepts `wantStrings` argument to conver buffers into strings var stripTags = map({wantStrings: true}, function (str) { // OMG don't actually use this return str.replace(/<.*?>/g, "") }) // Works like `Array.prototype.map` meaning you can specify a function that // takes up to two* arguments: fn(chunk, index) var spaceout = map({wantStrings: true}, function (chunk, index) { return (index % 2 == 0) ? chunk + "\n\n" : chunk }) // vs. with through2: var spaceout = through2(function (chunk, encoding, callback) { if (this.index == undefined) this.index = 0 var buf = (this.index++ % 2 == 0) ? Buffer.concat(chunk, new Buffer("\n\n")) : chunk this.push(buf) return callback() }) </pre></div> *Differences from <code>Array.prototype.map</code>: <ul> <li>Cannot insert <code>null</code> elements into the stream without aborting.</li> <li>No third <code>array</code> callback argument. That would require realizing the entire stream, which is generally counter-productive to stream operations.</li> <li><code>Array.prototype.map</code> doesn't modify the source Array, which is somewhat nonsensical when applied to streams.</li> </ul> <h2 id="options">Options</h2> <ul> <li>wantStrings: Automatically call chunk.toString() for the super lazy.</li> <li>all other through2 options</li> </ul> <h1 id="license">LICENSE</h1> MIT </div> </div> </body> </html>