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docs(ngFor): add documentation for ngForTrackBy (#10780) 

* docs(ngFor): add documentation for ngForTrackBy

* wo/ prefix
This commit is contained in:
Suguru Inatomi 2016-08-17 11:39:22 +09:00 committed by vikerman
parent 916ed55d82
commit 3c23238129
1 changed files with 14 additions and 3 deletions
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17
modules/@angular/common/src/directives/ng_for.ts
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@ -62,11 +62,22 @@ export class NgForRow {
* elements were deleted and all new elements inserted). This is an expensive operation and should * elements were deleted and all new elements inserted). This is an expensive operation and should
* be avoided if possible. * be avoided if possible.
* *
* To customize the default tracking algorithm, `NgFor` supports `trackBy` option.
* `trackBy` takes a function which has two arguments: `index` and `item`.
* If `trackBy` is given, Angular tracks changes by the return value of the function.
*
* ### Syntax * ### Syntax
* *
* - `<li *ngFor="let item of items; let i = index">...</li>` * - `<li *ngFor="let item of items; let i = index; trackBy: trackByFn">...</li>`
* - `<li template="ngFor let item of items; let i = index">...</li>` * - `<li template="ngFor let item of items; let i = index; trackBy: trackByFn">...</li>`
* - `<template ngFor let-item [ngForOf]="items" let-i="index"><li>...</li></template>` *
* With `<template>` element:
*
* ```
* <template ngFor let-item [ngForOf]="items" let-i="index" [ngForTrackBy]="trackByFn">
* <li>...</li>
* </template>
* ```
* *
* ### Example * ### Example
* *