feat(parse): ability to bind once an expressions #7486

lgalfaso · 2014-05-16T13:53:43Z

Expressions that start with :: will be binded once. The rule
that binding follows is that the binding will take the first
not-undefined value at the end of a $digest cycle.

Watchers from $watch, $watchCollection and $watchGroup will
automatically stop watching when the expression(s) are bind-once
and fulfill.

Watchers from text and attributes interpolations will
automatically stop watching when the expressions are fulfill.

All directives that use $parse for expressions will automatically
work with bind-once expressions as long as they are evaluated
over a $scope. E.g.

<div ng-bind="::foo"></div>
<li ng-repeat="item in ::items">{{::item.name}};</li>

Have fun

benchmark: http://plnkr.co/edit/rJOqa0oh35Y0xBhTYZ6w?p=info
design doc: https://docs.google.com/document/d/1fTqaaQYD2QE1rz-OywvRKFSpZirbWUPsnfaZaMq8fWI/edit#

mary-poppins · 2014-05-16T13:53:46Z

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

Uses the issue template (#7486)

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

IgorMinar · 2014-05-16T15:23:22Z

src/ng/parse.js

+        function result(self, locals) {
+          if (!stable) {
+            lastValue = expression(self, locals);
+            result.$$unwatch = isDefined(lastValue) && '$$unwatch';


what's the purpose of using the '$$unwatch' string literal as the value? why not just simple true?

I think that the chances of seeing an '$$unwatch' are smaller than true and will allow us to reuse the same property in the future

joshkurz · 2014-05-16T20:18:38Z

are there any plans to set up some official performance tests for this feature? It would be nice to see some tangible benefits. I know this is faster theoretically, but maybe having some benchmarks would be nice IMO.

IgorMinar · 2014-05-16T20:22:12Z

@joshkurz I don't think that making it configurable is that useful (unlike the interpolation markers). Everything inside of our interpolation markers should not be interpreted by anybody else, so you can think of it as an special operator in our expressions.

joshkurz · 2014-05-16T20:31:38Z

@IgorMinar that makes perfect sense.

On Fri, May 16, 2014 at 4:22 PM, Igor Minar notifications@git.luolix.topwrote:

@joshkurz https://github.com/joshkurz I don't think that making it
configurable is that useful (unlike the interpolation markers). Everything
inside of our interpolation markers should not be interpreted by anybody
else, so you can think of it as an special operator in our expressions.

—
Reply to this email directly or view it on GitHubhttps://github.com//pull/7486#issuecomment-43375243
.

Josh Kurz
www.joshkurz.net

IgorMinar · 2014-05-17T04:22:21Z

docs/content/guide/expression.ngdoc

+One-time binding expressions will retain the value of the expression at the end of the
+digest cycle as long as that value is not undefined. If the value of the expression is set
+within the digest loop and later, within the same digest loop, it is sent to undefined,
+then the expression is not fulfill and will remain watched. 


typo: "fulfilled"

IgorMinar · 2014-05-19T13:42:12Z

I mentioned earlier that we should consider throwing an error if one-time binding are used with ngModel. Since then I realized that there are some use-cases when you want to display a value via a possibly read-only input field and you want the value to be formatted, so I think we should allow it. So ignore my previous comment about throwing an error :)

IgorMinar · 2014-05-19T14:16:10Z

@joshkurz here is a benchmark: http://plnkr.co/edit/rJOqa0oh35Y0xBhTYZ6w

IgorMinar · 2014-05-19T15:36:06Z

btw the benchmark shows that our interpolation is 2x slower than direct binding via ngBind. 2x seems too much, so we should investigate why that's the case. but that's for another PR/issue

kseamon · 2014-05-19T15:51:50Z

src/ng/parse.js

@@ -1246,13 +1246,19 @@ function $ParseProvider() {
    };

    return function(exp) {
-      var parsedExpression;
+      var parsedExpression,
+        oneTime;


Don't know how much we care, but by the Google style guide, oneTime should be indented 4 rather than 2 spaces.

Expressions that start with `::` will be binded once. The rule that binding follows is that the binding will take the first not-undefined value at the end of a $digest cycle. Watchers from $watch, $watchCollection and $watchGroup will automatically stop watching when the expression(s) are bind-once and fulfill. Watchers from text and attributes interpolations will automatically stop watching when the expressions are fulfill. All directives that use $parse for expressions will automatically work with bind-once expressions. E.g. <div ng-bind="::foo"></div> <li ng-repeat="item in ::items">{{::item.name}};</li>

ermalmino · 2014-05-22T09:47:43Z

👍

Expressions that start with `::` will be binded once. The rule that binding follows is that the binding will take the first not-undefined value at the end of a $digest cycle. Watchers from $watch, $watchCollection and $watchGroup will automatically stop watching when the expression(s) are bind-once and fulfill. Watchers from text and attributes interpolations will automatically stop watching when the expressions are fulfill. All directives that use $parse for expressions will automatically work with bind-once expressions. E.g. <div ng-bind="::foo"></div> <li ng-repeat="item in ::items">{{::item.name}};</li> Paired with: Caitlin and Igor Design doc: https://docs.google.com/document/d/1fTqaaQYD2QE1rz-OywvRKFSpZirbWUPsnfaZaMq8fWI/edit# Closes angular#7486 Closes angular#5408

jimmywarting · 2014-05-25T18:59:18Z

Heven't done any benchmark but i tried the plnkr example. (Apart from the number of watcher and digest cycle benifit) It felt like the first bind/interpolate-once initialize took way longer then the first baseline-binding/interpolation initialization. (around 7-8 sec)
brings a couple of question:

Is it only me? can anyone else confirm this?
why is that?
what can we do to improve it?

Cinamonas · 2014-06-03T11:16:02Z

This is a very anticipated addition, but I encountered an issue where {{ ::foo }} fails with syntax error:

Syntax Error: Token ':' not a primary expression at column 2 of the expression

while {{::foo }} works correctly.

I believe this was not an intended behaviour?

lgalfaso · 2014-06-03T11:41:39Z

@Cinamonas #7640 took care of that, it should be part of the next beta

bolasblack · 2014-06-24T02:47:51Z

Wow ! Nice !

IgorMinar reviewed May 16, 2014
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IgorMinar reviewed May 17, 2014
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lgalfaso added cla: yes and removed cla: no labels May 19, 2014

kseamon reviewed May 19, 2014
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IgorMinar added this to the 1.3.0-beta.10 milestone May 19, 2014

ermalmino mentioned this pull request May 21, 2014

feat(ngShow,ngHide) bind to scope event expression evaluation #7531

Closed

caitp mentioned this pull request May 22, 2014

Feature: Enable disabling of two way bindings #7554

Closed

lgalfaso closed this in cee429f May 23, 2014

caitp mentioned this pull request May 28, 2014

Simplify watchGroupFn assignment using ternary #7619

Closed

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feat(parse): ability to bind once an expressions #7486

feat(parse): ability to bind once an expressions #7486

lgalfaso commented May 16, 2014

mary-poppins commented May 16, 2014

IgorMinar May 16, 2014

lgalfaso May 16, 2014

joshkurz commented May 16, 2014

IgorMinar commented May 16, 2014

joshkurz commented May 16, 2014

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kseamon May 19, 2014

ermalmino commented May 22, 2014

jimmywarting commented May 25, 2014

Cinamonas commented Jun 3, 2014

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bolasblack commented Jun 24, 2014

feat(parse): ability to bind once an expressions #7486

feat(parse): ability to bind once an expressions #7486

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lgalfaso commented May 16, 2014

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