Convert some usage of indexOf to startsWith/includes where applicable

In many cases in the code you don't actually care about the index itself, but rather just want to know if something exists in a String/Array or if a String starts in a particular way. With modern JavaScript functionality, it's thus possible to remove a number of existing `indexOf` cases.

src/core/evaluator.js

@@ -2533,13 +2533,12 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
         var fontNameStr = fontName && fontName.name;
         var baseFontStr = baseFont && baseFont.name;
         if (fontNameStr !== baseFontStr) {
-          info('The FontDescriptor\'s FontName is "' + fontNameStr +
-               '" but should be the same as the Font\'s BaseFont "' +
-               baseFontStr + '"');
+          info(`The FontDescriptor\'s FontName is "${fontNameStr}" but ` +
+               `should be the same as the Font\'s BaseFont "${baseFontStr}".`);
           // Workaround for cases where e.g. fontNameStr = 'Arial' and
           // baseFontStr = 'Arial,Bold' (needed when no font file is embedded).
           if (fontNameStr && baseFontStr &&
-              baseFontStr.indexOf(fontNameStr) === 0) {
+              baseFontStr.startsWith(fontNameStr)) {
             fontName = baseFont;
           }
         }

src/core/fonts.js

@@ -1200,7 +1200,7 @@ var Font = (function FontClosure() {
       // if at least one width is present, remeasure all chars when exists
       this.remeasure = Object.keys(this.widths).length > 0;
       if (isStandardFont && type === 'CIDFontType2' &&
-          this.cidEncoding.indexOf('Identity-') === 0) {
+          this.cidEncoding.startsWith('Identity-')) {
         var GlyphMapForStandardFonts = getGlyphMapForStandardFonts();
         // Standard fonts might be embedded as CID font without glyph mapping.
         // Building one based on GlyphMapForStandardFonts.

src/core/obj.js

@@ -701,10 +701,7 @@ class Catalog {
   static parseDestDictionary(params) {
     // Lets URLs beginning with 'www.' default to using the 'http://' protocol.
     function addDefaultProtocolToUrl(url) {
-      if (url.indexOf('www.') === 0) {
-        return `http://${url}`;
-      }
-      return url;
+      return (url.startsWith('www.') ? `http://${url}` : url);
     }
 
     // According to ISO 32000-1:2008, section 12.6.4.7, URIs should be encoded
@@ -1234,7 +1231,7 @@ var XRef = (function XRefClosure() {
         }
         var token = readToken(buffer, position);
         var m;
-        if (token.indexOf('xref') === 0 &&
+        if (token.startsWith('xref') &&
             (token.length === 4 || /\s/.test(token[4]))) {
           position += skipUntil(buffer, position, trailerBytes);
           trailers.push(position);
@@ -1288,7 +1285,7 @@ var XRef = (function XRefClosure() {
           }
 
           position += contentLength;
-        } else if (token.indexOf('trailer') === 0 &&
+        } else if (token.startsWith('trailer') &&
                    (token.length === 7 || /\s/.test(token[7]))) {
           trailers.push(position);
           position += skipUntil(buffer, position, startxrefBytes);
@@ -1507,7 +1504,7 @@ var XRef = (function XRefClosure() {
       }
       if (obj3.cmd !== 'obj') {
         // some bad PDFs use "obj1234" and really mean 1234
-        if (obj3.cmd.indexOf('obj') === 0) {
+        if (obj3.cmd.startsWith('obj')) {
           num = parseInt(obj3.cmd.substring(3), 10);
           if (!Number.isNaN(num)) {
             return num;

src/shared/fonts_utils.js

@@ -253,7 +253,7 @@ var Type2Parser = function type2Parser(aFilePath) {
   var xhr = new XMLHttpRequest();
   xhr.open('GET', aFilePath, false);
   xhr.responseType = 'arraybuffer';
-  xhr.expected = (document.URL.indexOf('file:') === 0) ? 0 : 200;
+  xhr.expected = document.URL.startsWith('file:') ? 0 : 200;
   xhr.send(null);
   this.data = new Stream(xhr.response);