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Templates and Logic

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Marco Otte-Witte @marcoow

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simplabs.com @simplabs

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No content

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https://ember-workshops.simplabs.com

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https://elixir-phoenix-workshops.simplabs.com

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Templates and Logic

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https://babeljs.io http://handlebarsjs.com http://blog.yhat.com/static/img/handlebars-logo.png

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"Handlebars.js is an extension to the Mustache templating language created by Chris Wanstrath. Handlebars.js and Mustache are both logicless templating languages that keep the view and the code separated like we all know they should be." https://github.com/wycats/handlebars.js/

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{{title}}

{{body}}
{ title: 'A post', body: 'Awesome post!' } + =

A post

Awesome post!

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{{title}}

{{body}}
{{#if author}}

{{author.firstName}} {{author.lastName}}

{{/if}}

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{{title}}

{{body}}
{{#if author}}

{{author.firstName}} {{author.lastName}}

{{/if}}

Comments

{{#each comments as |comment|}}

By {{comment.author}}

{{comment.text}}
{{/each}}

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{{title}}

{{body}}
{{#if author}}

{{fullName author}}

{{/if}}

Comments

{{#each comments as |comment|}}

By {{fullName comment.author}}

{{comment.text}}
{{/each}}

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…templates are not "logicless" but Handlebars.js itself is (more or less)

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in 2016 with Ember (and addons) you can do this:

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{{#each (take 1 (filter-by (shuffle users) 'isActive' true)) as |user|}} {{#let user.firstName user.lastName as |firstName lastName|}}

{{concat (capitalize firstName) ' ' (capitalize lastName)}} {{#if (and (eq (capitalize (take 1 firstName)) 'J') (lte user.age 65))}} (he's the special one!) {{/if}}

{{/let}} {{/each}}

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{{#each (take 1 (filter-by (shuffle model) 'isActive' true)) as |user|}} {{#let user.firstName user.lastName as |firstName lastName|}}

{{concat (capitalize firstName) ' ' (capitalize lastName)}} {{#if (and (eq (capitalize (take 1 firstName)) 'J') (lte user.age 65))}} (he's the special one!) {{/if}}

{{/let}} {{/each}}

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(he's the special one!)

https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/PHP-logo.svg/2000px-PHP-logo.svg.png http://vignette2.wikia.nocookie.net/villains/images/c/c8/TrollFace.png/revision/latest?cb=20150813022250

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it's fine (and necessary) to use logic in templates

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…but to what extent?

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export function gte([value, compareTo]) { return value >= compareTo; } export default Ember.Helper.helper(gte); {{#if (gte user.age 65)}} {{/if}} = {{#if user.isSenior}} {{/if}} isSenior: computed('age', function() { return this.get('age') >= 65; })

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export function gte([value, compareTo]) { return value >= compareTo; } export default Ember.Helper.helper(gte); {{#if (gte user.age 65)}} {{/if}} = {{#if user.isSenior}} {{/if}} isSenior: computed('age', function() { return gte(this.get(['age', 65])); })

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export function gte([value, compareTo]) { return value >= compareTo; } export default Ember.Helper.helper(gte); {{#if (gte user.age 65)}} {{/if}} = {{#if user.isSenior}} {{/if}} isSenior: computed.gte('age', 65)

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{{#each (filter-by users 'isActive' true) as |user|}} {{user.name}} {{/each}} = {{#each activeUsers as |user|}} {{user.name}} {{/each}} activeUsers: computed('[email protected]', function() { return this.get('users').filterBy('isActive', true); }) export function filterBy([collection, filterProperty, filterValue]) { return collection.filterBy(filterProperty, filterValue); } export default Ember.Helper.helper(filterBy);

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{{#each (filter-by users 'isActive' true) as |user|}} {{user.name}} {{/each}} = {{#each activeUsers as |user|}} {{user.name}} {{/each}} activeUsers: computed('[email protected]', function() { return filterBy([this.get('users'), 'isActive', true]); }) export function filterBy([collection, filterProperty, filterValue]) { return collection.filterBy(filterProperty, filterValue); } export default Ember.Helper.helper(filterBy);

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{{#each (filter-by users 'isActive' true) as |user|}} {{user.name}} {{/each}} = {{#each activeUsers as |user|}} {{user.name}} {{/each}} activeUsers: computed.filterBy('users', 'isActive', true) export function filterBy([collection, filterProperty, filterValue]) { return collection.filterBy(filterProperty, filterValue); } export default Ember.Helper.helper(filterBy);

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but what about helpers being pure?

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function fullName([firstName, lastName]) { return `${firstName} ${lastName}`; } fullName: computed('firstName', 'lastName', function() { return `${this.get('firstName')} ${this.get('lastName')}`; }) Inputs

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fullName: computed('firstName', 'lastName', function() { return `${this.get('firstName')} ${this.get('lastName')}`; }) import join from '../computeds/join'; … fullName: join('firstName', 'lastName') export default function join(first, second, glue = ' ') { let args = [first, second, function() { return [this.get(first), this.get(second)].join(glue); }]; return computed(...args); } =

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fullName: join('firstName', 'lastName', ' ') https://github.com/cibernox/ember-cpm

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export default Ember.Component.extend({ num1: 45, num2: 3.5, num3: 13.4, num4: -2, total: sum( sum('num1', 'num2', 'num3'), difference('num3', 'num2'), product(difference('num2', 'num1'), 'num4') ) }); https://github.com/cibernox/ember-cpm

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@computed('firstName', 'lastName') fullName(firstName, lastName) { return `${firstName} ${lastName}`; } https://github.com/rwjblue/ember-computed-decorators

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this topic is not limited to reactive logic

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Cancel Save

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Cancel Save save() { this._validate().then(() => { this.get('user').setProperties( this.getProperties('firstName', 'lastName') ); }).then(() => { return this.get('user').save(); }).then(() => { this.set('isEditing', false) }); } +

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Cancel Save + save() { pipe( () => this._validate(), () => this.get('user').setProperties(this.getProperties('firstName', 'lastName')), () => this.get('user').save(), () => this.set('isEditing', false) ); }

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Why is this all even relevant?

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There are a bunch of tradeoffs you need to be aware of

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Helpers might not always behave like you think they would

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export function isSenior([user]) { return user.get('age') >= 65; } export default Ember.Helper.helper(gte); {{#if (is-senior user)}} {{/if}}

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Computed Properties can easily be unit-tested - when using helpers you must render the template

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{{#each (filter-by users 'isActive' true) as |user|}} {{user.name}} {{/each}} export function filterBy([collection, filterProperty, filterValue]) { return collection.filterBy(filterProperty, filterValue); } export default Ember.Helper.helper(filterBy); This is what you want to test

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Helpers are harder to debug

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Separation of Concerns

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potential Maintainability issues

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{{#each (filter-by 'isActive' users true) as |user|}} {{user.name}} {{/each}}

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{{#each activeUsers as |user|}} {{user.name}} {{/each}} http://blog.yhat.com/static/img/handlebars-logo.png

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Cancel Save

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Cancel Save + save() { pipe( () => this._validate(), () => this.get('user').setProperties(this.getProperties('firstName', 'lastName')), () => this.get('user').save(), () => this.set('isEditing', false) ); }

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…so what's the advice?

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small demo project on github https://github.com/marcoow/templates-and-logic

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Thanks

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Q&A

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simplabs.com @simplabs