diff --git a/lib/font/afm.js b/lib/font/afm.js
index 610f381..ee5fd28 100644
--- a/lib/font/afm.js
+++ b/lib/font/afm.js
@@ -103,14 +103,16 @@ udieresis     yacute         thorn          ydieresis\
 `.split(/\s+/);
 
 class AFMFont {
+  /**
+   * @param {string} contents
+   */
   constructor(contents) {
-    this.contents = contents;
     this.attributes = {};
     this.glyphWidths = {};
     this.boundingBoxes = {};
     this.kernPairs = {};
 
-    this.parse();
+    this.parse(contents);
 
     this.bbox = this.attributes['FontBBox'].split(/\s+/).map((e) => +e);
     this.ascender = +(this.attributes['Ascender'] || 0);
@@ -121,9 +123,12 @@ class AFMFont {
       this.bbox[3] - this.bbox[1] - (this.ascender - this.descender);
   }
 
-  parse() {
+  /**
+   * @param {string} contents
+   */
+  parse(contents) {
     let section = '';
-    for (let line of this.contents.split('\n')) {
+    for (let line of contents.split('\n')) {
       var match;
       var a;
       if ((match = line.match(/^Start(\w+)/))) {
@@ -168,6 +173,10 @@ class AFMFont {
     }
   }
 
+  /**
+   * @param {string} text
+   * @returns
+   */
   encodeText(text) {
     const res = [];
     for (let i = 0, len = text.length; i < len; i++) {