javascript - Lodash - can you continue chaining after variable declaration? -


this bit of code:

var foo = [1, 2, 3],     bar = _.chain(foo)             .map(number => number * 2);   console.log(bar.value());  bar.tap(numbers =>  {   numbers.push(10000); });  console.log(bar.value());

the 10000 won't added bar.value(). if move tap chain during actual variable chain, works fine. i'm has context of tap called, can explain? seems nice init chain , modify later. thanks!

bin demonstration: http://jsbin.com/kidomeqalo/edit?html,js,console

js bin on jsbin.com

just adding bar.tap(); doesn't change anything. need include in chain:

bar = bar.tap(numbers =>  {   numbers.push(10000); }); console.log(bar.value());

or

console.log(bar.tap(numbers =>  {   numbers.push(10000); }).value());

on top of that, should not use tap executing side effects. rather use bar.concat(10000).value() or that, makes clear creates new result in functional way instead of mutating - becomes confusing sequences evaluated lazily.


-

Comments

Post a Comment

Popular posts from this blog

amazon web services - S3 Pre-signed POST validate file type? -

i know it's possible put limit on file size content-length-range header. possible validate file type? https://docs.aws.amazon.com/amazons3/latest/dev/httppostforms.html#policyconditions i see there content-type header, if set say, audio/mp3 allow mp3 files , return error if file not mp3? i found previous question answers mention validating file size: s3 direct upload restricting file size , type you can specify content-type @ post request. you can specify @ signature, post must done content-type: { "expiration": "2007-12-01t12:00:00.000z", "conditions": [ {"acl": "public-read" }, {"bucket": "johnsmith" }, {"content-type: "audio/mp3"} ] } creating html form (using aws signature version 4) edit: @ previous question found, checking content-type.
Read more

c# - Check Keyboard Input Winforms -

i wondering if instead of doing this protected override void onkeydown(keyeventargs e) { if (e.keycode == keys.a) console.writeline("the key down."); } i set bool method , this: if(keydown(keys.a)) // whatever here i've been sitting here ages trying figure out how it. can't wrap head around it. in case wondering, plan call bool inside different method, check input. since want perform action after pressing key, using keydown event enough. but in cases suppose want check if specific key down in middle of process, can use getkeystate method way: [dllimport("user32.dll", charset = charset.auto, exactspelling = true)] public static extern short getkeystate(int keycode); public const int key_pressed = 0x8000; public static bool iskeydown(keys key) { return convert.toboolean(getkeystate((int)key) & key_pressed); } you should know, each time check key state using example iskeydown(keys.a) method returns true if ke...
Read more