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# String Formatting
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Essential tools for formatted string output and detailed object inspection with customizable styling and output options.
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## Capabilities
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### Format Function
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Printf-style string formatting with placeholder substitution.
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```javascript { .api }
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/**
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 * Formats a string using printf-style placeholders
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 * @param {string} f - Format string with placeholders (%s, %d, %j, %%)
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 * @param {...any} args - Arguments to substitute into placeholders
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 * @returns {string} Formatted string
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 */
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function format(f, ...args): string;
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```
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Supported placeholders:
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- `%s` - String conversion
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- `%d` - Number conversion  
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- `%j` - JSON.stringify conversion
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- `%%` - Literal percent sign
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**Usage Examples:**
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```javascript
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const util = require('util');
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// Basic formatting
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util.format('Hello %s', 'world'); // "Hello world"
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util.format('Number: %d', 42); // "Number: 42"
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util.format('JSON: %j', { a: 1 }); // "JSON: {"a":1}"
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util.format('Percent: %%'); // "Percent: %"
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// Multiple placeholders
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util.format('%s is %d years old', 'Alice', 25); // "Alice is 25 years old"
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// Extra arguments are appended
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util.format('%s %s', 'a', 'b', 'c'); // "a b c"
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// Non-string format argument
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util.format(123, 'abc'); // "123 abc"
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```
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### Inspect Function
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Returns a string representation of objects with detailed formatting options.
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```javascript { .api }
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/**
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 * Returns a string representation of an object
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 * @param {any} obj - Object to inspect
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 * @param {InspectOptions} [opts] - Inspection options
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 * @returns {string} String representation of the object
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 */
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function inspect(obj, opts?): string;
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interface InspectOptions {
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  /** Show hidden (non-enumerable) properties */
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  showHidden?: boolean;
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  /** Recursion depth (default: 2) */
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  depth?: number;
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  /** Use ANSI color codes for styling */
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  colors?: boolean;
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  /** Enable custom inspect functions */
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  customInspect?: boolean;
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}
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```
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**Usage Examples:**
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```javascript
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const util = require('util');
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const obj = {
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  name: 'example',
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  data: { numbers: [1, 2, 3], active: true },
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  method: function() { return 'hello'; }
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};
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// Basic inspection
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console.log(util.inspect(obj));
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// With colors (for terminal output)
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console.log(util.inspect(obj, { colors: true }));
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// Show hidden properties
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console.log(util.inspect(obj, { showHidden: true }));
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// Control depth
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console.log(util.inspect(obj, { depth: 1 }));
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// Inspect primitive values
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util.inspect(123); // "123"
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util.inspect('hello'); // "'hello'"
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util.inspect(true); // "true"
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util.inspect(null); // "null"
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```
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### Inspect Styling
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Configuration objects for customizing inspect output appearance.
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```javascript { .api }
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// Color codes for ANSI styling
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inspect.colors: {
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  bold: [number, number];
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  italic: [number, number];
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  underline: [number, number];
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  inverse: [number, number];
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  white: [number, number];
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  grey: [number, number];
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  black: [number, number];
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  blue: [number, number];
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  cyan: [number, number];
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  green: [number, number];
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  magenta: [number, number];
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  red: [number, number];
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  yellow: [number, number];
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};
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// Style mappings for different value types
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inspect.styles: {
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  special: string;
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  number: string;
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  boolean: string;
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  undefined: string;
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  null: string;
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  string: string;
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  date: string;
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  regexp: string;
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};
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```
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**Usage Examples:**
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```javascript
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const util = require('util');
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// Customize colors
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util.inspect.colors.custom = [95, 39]; // Custom color code
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util.inspect.styles.myType = 'custom';
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// Default color mappings
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console.log(util.inspect.styles.number); // "yellow"
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console.log(util.inspect.styles.string); // "green"
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console.log(util.inspect.styles.boolean); // "yellow"
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```