Instantiating LinkifyIt lazily, only if needed

lib/common/utils.js

@@ -39,6 +39,24 @@ function arrayReplaceAt(src, pos, newElements) {
   return [].concat(src.slice(0, pos), newElements, src.slice(pos + 1));
 }
 
+// Sets a property whose initial is computed lazily on an target object
+function defineLazyProperty(target, property, instantiator) {
+  var initied = false;
+  var value;
+  Object.defineProperty(target, property, {
+    get: function () {
+      if (initied) return value;
+      initied = true;
+      value = instantiator();
+      return value;
+    },
+    set: function (newValue) {
+      initied = true;
+      value = newValue;
+    }
+  });
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 function isValidEntityCode(c) {
@@ -300,6 +318,7 @@ exports.lib.mdurl           = require('mdurl');
 exports.lib.ucmicro         = require('uc.micro');
 
 exports.assign              = assign;
+exports.defineLazyProperty  = defineLazyProperty;
 exports.isString            = isString;
 exports.has                 = has;
 exports.unescapeMd          = unescapeMd;

lib/index.js

@@ -9,7 +9,6 @@ var Renderer     = require('./renderer');
 var ParserCore   = require('./parser_core');
 var ParserBlock  = require('./parser_block');
 var ParserInline = require('./parser_inline');
-var LinkifyIt    = require('linkify-it');
 var mdurl        = require('mdurl');
 var punycode     = require('punycode');
 
@@ -288,7 +287,10 @@ function MarkdownIt(presetName, options) {
    * Used by [linkify](https://github.com/markdown-it/markdown-it/blob/master/lib/rules_core/linkify.js)
    * rule.
    **/
-  this.linkify = new LinkifyIt();
+  utils.defineLazyProperty(this, 'linkify', function () {
+    var LinkifyIt = require('linkify-it');
+    return new LinkifyIt();
+  });
 
   /**
    * MarkdownIt#validateLink(url) -> Boolean