Syntax Highlighter For JavaScript Snippets – Syntax.js

A minimal syntax highlighter with line numbers specifically designed for JavaScript source code snippets.

How to use it:

1. Insert the main script Syntax.js into the HTML page.

<script src="js/syntax.min.js"></script>

2. Insert your JavaScript source code snippets into a code element.

<code>
(() => {
const reservedWords = [
    "abstract", "arguments", "await", "boolean", "break", "byte", "case", "catch", "char", "class", "const", "continue", "debugger",
    "default", "delete", "do", "double", "else", "enum", "eval", "export", "extends", "false", "final", "finally", "float", "for",
    "function", "goto", "if", "implements", "import", "in", "instanceof", "int", "interface", "let", "long", "native", "new", "null",
    "package", "private", "protected", "public", "return", "short", "static", "super", "switch", "synchronized", "this", "throw",
    "throws", "transient", "true", "try", "typeof", "var", "void", "volatile", "while", "with", "yield"
]
const objectsPropertiesMethods = [
    "Array", "Date", "hasOwnProperty", "Infinity", "isFinite", "isNaN", "isPrototypeOf", "length", "Math", "NaN", "name", "Number",
    "Object", "prototype", "String", "toString", "undefined", "valueOf"
]
const rules = [
    {regex: `\\b(${reservedWords.join('|')})\\b`, params: ['g'], replaceWith: '¹$1¹'},
    {regex: `\\b(${objectsPropertiesMethods.join('|')})\\b`, params: ['g'], replaceWith: '²$1²'},
    {regex: '(\'.*\')|(\".*\")|(\`.*\`)', params: ['g'], replaceWith: '³$&³'},
    {regex: '(\\$\{.*\})', params: ['g'], replaceWith: '¹$1¹'},
    {regex: '(\#.*)', params: ['g'], replaceWith: '⁴$1⁴'},
    {regex: '¹([^¹]*)¹', params: ['g'], replaceWith: '<spam class="reserved">$1</spam>'},
    {regex: '²([^²]*)²', params: ['g'], replaceWith: '<spam class="methods">$1</spam>'},
    {regex: '³([^³]*)³', params: ['g'], replaceWith: '<spam class="variable">$1</spam>'},
    {regex: '⁴([^⁴]*)⁴', params: ['g'], replaceWith: '<spam class="comment">$1</spam>'},
    {regex: '(/\\*[^*]*\\*+(?:[^/*][^*]*\\*+)*/)', params: ['g'], replaceWith: '<spam class="comment">$1</spam>'},
    {regex: '([+-]?([0-9]*[.])?[0-9]+)', params: ['g'], replaceWith: '<spam class="number">$1</spam>'},
]
const format = (code) => {
    let text = code.innerText.trim()
    for(const rule of rules)
        text = text.replace(new RegExp(rule.regex, ...rule.params), rule.replaceWith)
    return text.split(/\n/).map(line => `<div>${line}</div>`).join('')
}
const formatAll = () => {
    for(const code of document.querySelectorAll('code'))
        code.innerHTML = format(code)
}
formatAll()
})()
</code>

3. Apply custom styles to the Syntax Highlighter.

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  color: #EEE;
  background-color: #333;
  padding: 10px;
  font-size: 105%;
  display: block;
  white-space: pre;
  counter-reset: line;
  overflow: auto;
}
code > div {
  counter-increment: line;
  display: block;
  min-height: 1em;
}
code > div::before {
  content: counter(line) '\A0';
  display: inline-block;
  width: 4ch;
  text-align: left;
  -webkit-select: none;
  color: #666;
}
.reserved {
  font-weight: bold;
  color: #3498DB;
}
.methods {
  font-weight: bold;
  color: #1ABC9C;
}
.variable {
  color: orange;
}
.comment {
  color: gray;
}
.number {
  color: red;
}