Print the result of evaluated expressions
📦 Node.js-> Command Line
✨ The Prompt Phrase
node -p "2 + 2"
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</head>
<body>
<div class="progress-container">
<div class="progress-bar" id="progressBar"></div>
</div>
<div class="hero">
<div class="hero-content">
<div class="print-icon">🖨️</div>
<h1>Master node -p Command!</h1>
<div class="command-display">node -p "2 + 2"</div>
<p>Print JavaScript results instantly! 🚀</p>
</div>
</div>
<div class="container">
<!-- What Is It -->
<section class="section">
<h2 class="section-title">🤔 What Is This Command?</h2>
<div class="card">
<p style="font-size: 1.2rem; margin-bottom: 20px;">
This command tells Node.js to <span class="highlight">evaluate</span> JavaScript code and <strong>automatically print</strong> the result! 🖨️
</p>
<p style="margin-bottom: 20px;">
Think of it like a super-smart calculator! 🧮 You type an expression, and Node.js instantly shows you the answer. No <code>console.log()</code> needed!
</p>
<div class="info">
<strong>Breaking It Down:</strong>
<ul style="margin-left: 30px; margin-top: 10px; line-height: 2;">
<li><code>node</code> - The Node.js runtime</li>
<li><code class="code-flag">-p</code> - Flag that means "print" (evaluate and print result)</li>
<li><code class="code-string">"2 + 2"</code> - The JavaScript expression to evaluate</li>
<li>Output: <code class="code-output">4</code> appears instantly!</li>
</ul>
</div>
<div style="margin-top: 30px;">
<h3 style="color: var(--accent-pink); margin-bottom: 15px;">How is -p different from -e? 🔍</h3>
<div class="comparison-box">
<div class="comparison-item">
<h4>node -e</h4>
<p><code>node -e "console.log(2+2)"</code></p>
<p style="margin-top: 10px; color: var(--text-secondary);">Requires console.log() to see output</p>
</div>
<div class="comparison-item highlight">
<h4>node -p ⭐</h4>
<p><code>node -p "2+2"</code></p>
<p style="margin-top: 10px; color: var(--text-secondary);">Automatically prints the result!</p>
</div>
</div>
</div>
</div>
</section>
<!-- Why Use It -->
<section class="section">
<h2 class="section-title">✨ Why Use node -p?</h2>
<div class="card">
<div class="feature-grid">
<div class="feature-card">
<div class="feature-icon">⚡</div>
<div class="feature-title">Instant Results</div>
<p style="color: var(--text-secondary);">No console.log needed!</p>
</div>
<div class="feature-card">
<div class="feature-icon">🧮</div>
<div class="feature-title">Quick Calculator</div>
<p style="color: var(--text-secondary);">Math on the fly!</p>
</div>
<div class="feature-card">
<div class="feature-icon">🔍</div>
<div class="feature-title">Expression Testing</div>
<p style="color: var(--text-secondary);">Test code snippets!</p>
</div>
<div class="feature-card">
<div class="feature-icon">📜</div>
<div class="feature-title">Shell Scripts</div>
<p style="color: var(--text-secondary);">Perfect for automation!</p>
</div>
<div class="feature-card">
<div class="feature-icon">🎯</div>
<div class="feature-title">One-Liners</div>
<p style="color: var(--text-secondary);">Shorter commands!</p>
</div>
<div class="feature-card">
<div class="feature-icon">🚀</div>
<div class="feature-title">Fast Debugging</div>
<p style="color: var(--text-secondary);">Check values instantly!</p>
</div>
</div>
</div>
</section>
<!-- How It Works -->
<section class="section">
<h2 class="section-title">⚙️ How Does It Work?</h2>
<div class="card">
<div class="steps">
<div class="step">
<h3>Step 1: Command Parsed</h3>
<p>Your terminal reads the command and identifies the -p flag.</p>
</div>
<div class="step">
<h3>Step 2: Node.js Starts</h3>
<p>Node.js runtime initializes in "print" mode.</p>
</div>
<div class="step">
<h3>Step 3: Expression Evaluated</h3>
<p>The JavaScript expression is evaluated by V8 engine.</p>
</div>
<div class="step">
<h3>Step 4: Result Computed</h3>
<p>The expression produces a result value (e.g., 2 + 2 = 4).</p>
</div>
<div class="step">
<h3>Step 5: Auto-Print</h3>
<p>Node.js automatically prints the result to stdout.</p>
</div>
<div class="step">
<h3>Step 6: Process Exits</h3>
<p>Node.js completes and returns to terminal! 🎉</p>
</div>
</div>
</div>
</section>
<!-- Live Demo -->
<section class="section">
<h2 class="section-title">🎮 Interactive Calculator</h2>
<div class="demo-container">
<h3 style="margin-bottom: 20px; font-size: 1.5rem;">Try Your Own Expressions! 🚀</h3>
<div class="calculator">
<div class="calc-display" id="calcDisplay">Ready to calculate...</div>
<input type="text" class="calc-input" id="calcInput" placeholder='Try: 2 + 2, Math.PI, "hello".toUpperCase()' value="2 + 2">
<button class="calc-button" onclick="calculateExpression()">🖨️ Print Result (node -p)</button>
</div>
<div style="margin-top: 30px;">
<h4 style="margin-bottom: 15px;">Quick Examples:</h4>
<button class="demo-button" onclick="simulateMath()">
<span>🧮</span>
<span>Math Operations</span>
</button>
<button class="demo-button" onclick="simulateString()">
<span>📝</span>
<span>String Methods</span>
</button>
<button class="demo-button" onclick="simulateArray()">
<span>📊</span>
<span>Array Operations</span>
</button>
</div>
<div class="terminal" id="terminal">
<div class="terminal-line">
<span class="terminal-prompt">$</span>
<span style="color: var(--text-secondary);"> Ready to print results...</span>
</div>
</div>
</div>
</section>
<!-- Code Breakdown -->
<section class="section">
<h2 class="section-title">💻 Command Examples</h2>
<div class="card">
<div class="tabs">
<button class="tab active" onclick="switchTab('math')">Math</button>
<button class="tab" onclick="switchTab('strings')">Strings</button>
<button class="tab" onclick="switchTab('arrays')">Arrays</button>
<button class="tab" onclick="switchTab('advanced')">Advanced</button>
</div>
<div id="math" class="tab-content active">
<h3 style="color: var(--accent-pink); margin-bottom: 15px;">Math Operations</h3>
<div class="code-block">
<div class="code-header">
<div class="terminal-dots">
<div class="terminal-dot dot-red"></div>
<div class="terminal-dot dot-yellow"></div>
<div class="terminal-dot dot-green"></div>
</div>
<button class="copy-btn" onclick="copyCode('math-code')">📋 Copy</button>
</div>
<pre><code id="math-code"><span class="code-comment"># Basic arithmetic</span>
node -p "2 + 2" <span class="code-comment"># Output: 4</span>
node -p "10 * 5" <span class="code-comment"># Output: 50</span>
node -p "100 / 4" <span class="code-comment"># Output: 25</span>
<span class="code-comment"># Math constants and functions</span>
node -p "Math.PI" <span class="code-comment"># Output: 3.141592653589793</span>
node -p "Math.sqrt(144)" <span class="code-comment"># Output: 12</span>
node -p "Math.random()" <span class="code-comment"># Output: random number</span>
<span class="code-comment"># Complex expressions</span>
node -p "(5 + 3) * 2" <span class="code-comment"># Output: 16</span></code></pre>
</div>
<div class="success" style="margin-top: 15px;">
<strong>Result:</strong> Instant calculations without opening a calculator!
</div>
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<h3 style="color: var(--accent-pink); margin-bottom: 15px;">String Operations</h3>
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<pre><code id="strings-code"><span class="code-comment"># String methods</span>
node -p "'hello'.toUpperCase()" <span class="code-comment"># HELLO</span>
node -p "'WORLD'.toLowerCase()" <span class="code-comment"># world</span>
node -p "'hello world'.split(' ')" <span class="code-comment"># [ 'hello', 'world' ]</span>
<span class="code-comment"># String manipulation</span>
node -p "'hello' + ' ' + 'world'" <span class="code-comment"># hello world</span>
node -p "'javascript'.length" <span class="code-comment"># 10</span>
node -p "'hello'.repeat(3)" <span class="code-comment"># hellohellohello</span>
<span class="code-comment"># Template literals</span>
node -p "\`2 + 2 = \${2 + 2}\`" <span class="code-comment"># 2 + 2 = 4</span></code></pre>
</div>
<div class="tip" style="margin-top: 15px;">
<strong>Pro Tip:</strong> Use single quotes inside double quotes for strings!
</div>
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<h3 style="color: var(--accent-pink); margin-bottom: 15px;">Array Operations</h3>
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<pre><code id="arrays-code"><span class="code-comment"># Array methods</span>
node -p "[1,2,3].length" <span class="code-comment"># 3</span>
node -p "[1,2,3].map(x => x * 2)" <span class="code-comment"># [ 2, 4, 6 ]</span>
node -p "[1,2,3,4,5].filter(x => x > 2)" <span class="code-comment"># [ 3, 4, 5 ]</span>
<span class="code-comment"># Array operations</span>
node -p "[1,2,3].join('-')" <span class="code-comment"># 1-2-3</span>
node -p "[1,2,3].reverse()" <span class="code-comment"># [ 3, 2, 1 ]</span>
node -p "[1,2,3,4,5].slice(1,3)" <span class="code-comment"># [ 2, 3 ]</span>
<span class="code-comment"># Reduce for sum</span>
node -p "[1,2,3,4,5].reduce((a,b)=>a+b)" <span class="code-comment"># 15</span></code></pre>
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<div id="advanced" class="tab-content">
<h3 style="color: var(--accent-pink); margin-bottom: 15px;">Advanced Usage</h3>
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<pre><code id="advanced-code"><span class="code-comment"># JSON operations</span>
node -p "JSON.stringify({name:'Alice',age:30})"
node -p "JSON.parse('{\"x\":10}').x"
<span class="code-comment"># Date operations</span>
node -p "new Date().getFullYear()"
node -p "new Date().toISOString()"
<span class="code-comment"># Regular expressions</span>
node -p "/\d+/.test('abc123')" <span class="code-comment"># true</span>
node -p "'hello123'.match(/\d+/)" <span class="code-comment"># [ '123' ]</span>
<span class="code-comment"># Environment variables</span>
node -p "process.platform" <span class="code-comment"># darwin/linux/win32</span>
node -p "process.version" <span class="code-comment"># v18.x.x</span></code></pre>
</div>
</div>
</div>
</section>
<!-- Common Mistakes -->
<section class="section">
<h2 class="section-title">❌ Common Mistakes</h2>
<div class="card">
<div class="accordion">
<div class="accordion-item">
<div class="accordion-header" onclick="toggleAccordion(this)">
<span><strong>1. Using console.log() with -p</strong></span>
<span class="accordion-icon">▼</span>
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<div class="accordion-content">
<div class="accordion-body">
<div class="warning">
<strong>Problem:</strong> <code>node -p "console.log(2+2)"</code> prints "undefined"!
</div>
<div class="success" style="margin-top: 15px;">
<strong>Solution:</strong> Just use <code>node -p "2+2"</code> - no console.log needed!
</div>
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</div>
<div class="accordion-item">
<div class="accordion-header" onclick="toggleAccordion(this)">
<span><strong>2. Forgetting Quotes</strong></span>
<span class="accordion-icon">▼</span>
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<div class="accordion-content">
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<div class="warning">
<strong>Problem:</strong> <code>node -p 2+2</code> won't work!
</div>
<div class="success" style="margin-top: 15px;">
<strong>Solution:</strong> Always wrap in quotes: <code>node -p "2+2"</code>
</div>
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<span><strong>3. Expecting Multiple Statements</strong></span>
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<strong>Problem:</strong> -p only prints the LAST expression result!
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<strong>Solution:</strong> Use -e for multiple statements or combine into one expression!
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<h2 class="section-title">🚀 Pro Tips</h2>
<div class="card">
<div class="tip">
<strong>Quick calculator</strong> - Use as instant calculator: <code>node -p "Math.sqrt(144)"</code>
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<div class="tip">
<strong>Shell scripting</strong> - Perfect for bash scripts: <code>RESULT=$(node -p "2+2")</code>
</div>
<div class="tip">
<strong>JSON parsing</strong> - Parse JSON quickly: <code>echo '{"x":5}' | node -p "JSON.parse(require('fs').readFileSync(0)).x"</code>
</div>
<div class="tip">
<strong>Date formatting</strong> - Get timestamps: <code>node -p "Date.now()"</code>
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<strong>Random generation</strong> - Generate random IDs: <code>node -p "Math.random().toString(36).substr(2,9)"</code>
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<strong>Create aliases</strong> - Add to .bashrc: <code>alias calc='node -p'</code> then use <code>calc "2+2"</code>
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<h3>Question 1: What does the -p flag do?</h3>
<div class="quiz-options">
<div class="quiz-option" onclick="checkAnswer(this, false, 1)">A) Prints error messages</div>
<div class="quiz-option" onclick="checkAnswer(this, true, 1)">B) Evaluates and automatically prints the result</div>
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<h3>Question 2: Which command is correct?</h3>
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<div class="quiz-option" onclick="checkAnswer(this, false, 2)">A) node -p console.log(2+2)</div>
<div class="quiz-option" onclick="checkAnswer(this, true, 2)">B) node -p "2+2"</div>
<div class="quiz-option" onclick="checkAnswer(this, false, 2)">C) node -p 2+2</div>
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<h3>Question 3: What's the output of: node -p "5 * 3"</h3>
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<div class="quiz-option" onclick="checkAnswer(this, true, 3)">B) 15</div>
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<h2 class="section-title">📚 Quick Reference</h2>
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<h3 style="margin-bottom: 20px; font-size: 2rem;">node -p Cheat Sheet! 🔖</h3>
<div class="cheat-grid">
<div class="cheat-item">
<h4>🖨️ Basic Print</h4>
<p><code>node -p "2+2"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">Output: 4</p>
</div>
<div class="cheat-item">
<h4>🧮 Math</h4>
<p><code>node -p "Math.PI"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">Constants & functions</p>
</div>
<div class="cheat-item">
<h4>📝 Strings</h4>
<p><code>node -p "'hi'.toUpperCase()"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">String methods</p>
</div>
<div class="cheat-item">
<h4>📊 Arrays</h4>
<p><code>node -p "[1,2,3].length"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">Array operations</p>
</div>
<div class="cheat-item">
<h4>📅 Date</h4>
<p><code>node -p "new Date().getFullYear()"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">Current year</p>
</div>
<div class="cheat-item">
<h4>🎲 Random</h4>
<p><code>node -p "Math.random()"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">Random numbers</p>
</div>
<div class="cheat-item">
<h4>📦 JSON</h4>
<p><code>node -p "JSON.stringify({x:1})"</code></p>
<p style="font-size: 0.85rem; margin-top: 5px;">JSON operations</p>
</div>
<div class="cheat-item">
<h4>⚙️ vs -e</h4>
<p>-p auto-prints, -e needs console.log</p>
<p style="font-size: 0.85rem; margin-top: 5px;">Key difference</p>
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<p style="font-size: 1.2rem; margin-bottom: 20px;">You now understand <strong>node -p</strong>! 🚀</p>
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