CODEWITHSUNDEEP
cssexpressionpolymer
Jorge Hernandez
Jorge Hernandez

Reputation: 187

Conditionally add css class in polymer

I have an element inside a polymer component and want to add a css class conditionally.

<div class="bottom {{completed: item.completed}}">

if item.isCompleted is true, then add the .completed class.

However, I've got the following error:

Invalid expression syntax: completed?: item.completed

I don't want to put the hole subtree inside a template conditional. Is it possible to do using an expression inside an html tag? I'm using the last polymer release, is this funtionallity migrated or replaced in any way?

Upvotes: 15

Views: 15657

Answers (3)

AlexO
AlexO

Reputation: 1444

The tokenlist technique was valid in Polymer 0.5, but has been deprecated.

As of Polymer 1.2, the following works:

<dom-module ...>
  <template>
    <div class$="bottom [[conditionalClass(item.completed)]]"></div>
  </template>
  <script>
    Polymer({
      ...
      conditionalClass: function(completed) {
        return completed ? 'completed' : '';
      }
    });
  <script>
</dom-module>

Also see similar question: Polymer 1.0 - Binding css classes

Upvotes: 18

G&#252;nter Z&#246;chbauer
G&#252;nter Z&#246;chbauer

Reputation: 657666

update Polymer 1.0

<div class$="[[getClasses(item.completed)]]">

getClasses: function (completed) {
  var classes = 'bottom'
  if(completed) classes += ' completed';
  return classes;
}

Even when completed could be read from this.item.completed inside getClasses() it's important to pass it as parameter from the binding. This way Polymer re-evaluates the function getClasses(item.completed) each time item.completed changed.

original - Polymer 0.5

It should look like

<div class="bottom {{ {completed: item.completed } | tokenList }}">

See docs for more details: http://polymer-project.org/docs/polymer/expressions.html#tokenlist

Upvotes: 13

Adriano Spadoni
Adriano Spadoni

Reputation: 4790

the simplest way to do it:

<template>
  <style is="custom-style">
      .item-completed-true { background: red; }
  </style>
  <div class$="bottom item-completed-[[item.completed]]"></div>
</template>

Upvotes: 3

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