AttributePool: Use ES6 class syntax

src/static/js/AttributePool.js

@@ -29,13 +29,14 @@
   used to reference Attributes in Changesets.
 */
 
-const AttributePool = function () {
+class AttributePool {
+  constructor() {
     this.numToAttrib = {}; // e.g. {0: ['foo','bar']}
     this.attribToNum = {}; // e.g. {'foo,bar': 0}
     this.nextNum = 0;
-};
+  }
 
-AttributePool.prototype.putAttrib = function (attrib, dontAddIfAbsent) {
+  putAttrib(attrib, dontAddIfAbsent = false) {
     const str = String(attrib);
     if (str in this.attribToNum) {
       return this.attribToNum[str];
@@ -47,43 +48,43 @@ AttributePool.prototype.putAttrib = function (attrib, dontAddIfAbsent) {
     this.attribToNum[str] = num;
     this.numToAttrib[num] = [String(attrib[0] || ''), String(attrib[1] || '')];
     return num;
-};
+  }
 
-AttributePool.prototype.getAttrib = function (num) {
+  getAttrib(num) {
     const pair = this.numToAttrib[num];
     if (!pair) {
       return pair;
     }
     return [pair[0], pair[1]]; // return a mutable copy
-};
+  }
 
-AttributePool.prototype.getAttribKey = function (num) {
+  getAttribKey(num) {
     const pair = this.numToAttrib[num];
     if (!pair) return '';
     return pair[0];
-};
+  }
 
-AttributePool.prototype.getAttribValue = function (num) {
+  getAttribValue(num) {
     const pair = this.numToAttrib[num];
     if (!pair) return '';
     return pair[1];
-};
+  }
 
-AttributePool.prototype.eachAttrib = function (func) {
+  eachAttrib(func) {
     for (const n of Object.keys(this.numToAttrib)) {
       const pair = this.numToAttrib[n];
       func(pair[0], pair[1]);
     }
-};
+  }
 
-AttributePool.prototype.toJsonable = function () {
+  toJsonable() {
     return {
       numToAttrib: this.numToAttrib,
       nextNum: this.nextNum,
     };
-};
+  }
 
-AttributePool.prototype.fromJsonable = function (obj) {
+  fromJsonable(obj) {
     this.numToAttrib = obj.numToAttrib;
     this.nextNum = obj.nextNum;
     this.attribToNum = {};
@@ -91,7 +92,7 @@ AttributePool.prototype.fromJsonable = function (obj) {
       this.attribToNum[String(this.numToAttrib[n])] = Number(n);
     }
     return this;
-};
+  }
-
+}
 
 module.exports = AttributePool;