Rolling forward https://codereview.chromium.org/1155683008/ which was

third_party/polymer/v0_8/components-chromium/iron-range-behavior/iron-range-behavior-extracted.js

-
-
- /** 
- * `iron-range-behavior` provides the behavior for something with a minimum to maximum range.
- *
- * @demo demo/index.html
- * @polymerBehavior 
- */
- Polymer.IronRangeBehavior = {
-
-  properties: {
-
-    /**
-     * The number that represents the current value.
-     */
-    value: {
-      type: Number,
-      value: 0,
-      notify: true,
-      reflectToAttribute: true
-    },
-
-    /**
-     * The number that indicates the minimum value of the range.
-     */
-    min: {
-      type: Number,
-      value: 0,
-      notify: true
-    },
-
-    /**
-     * The number that indicates the maximum value of the range.
-     */
-    max: {
-      type: Number,
-      value: 100,
-      notify: true
-    },
-
-    /**
-     * Specifies the value granularity of the range's value.
-     */
-    step: {
-      type: Number,
-      value: 1,
-      notify: true
-    },
-
-    /**
-     * Returns the ratio of the value.
-     */
-    ratio: {
-      type: Number,
-      value: 0,
-      readOnly: true,
-      notify: true
-    },
-  },
-
-  observers: [
-    '_update(value, min, max, step)'
-  ],
-
-  _calcRatio: function(value) {
-    return (this._clampValue(value) - this.min) / (this.max - this.min);
-  },
-
-  _clampValue: function(value) {
-    return Math.min(this.max, Math.max(this.min, this._calcStep(value)));
-  },
-
-  _calcStep: function(value) {
-    return this.step ? (Math.round(value / this.step) / (1 / this.step)) : value;
-  },
-
-  _validateValue: function() {
-    var v = this._clampValue(this.value);
-    this.value = this.oldValue = isNaN(v) ? this.oldValue : v;
-    return this.value !== v;
-  },
-
-  _update: function() {
-    this._validateValue();
-    this._setRatio(this._calcRatio(this.value) * 100);
-  }
-
-};