Classnames

mediumcodingJavaScriptStringsObjects~25 min

Asked at Meta, Vercel, Shopify

Overview

Implement classnames(...args) that joins class names. Supports strings, objects (keys with truthy values), and arrays.

Examples

classnames('foo', { bar: true, baz: false }, 'qux'); // 'foo bar qux'
classnames('a', ['b', { c: true }]); // 'a b c'

Solution

Reveal solution

function classnames(...args) {
  const classes = [];
  for (const arg of args) {
    if (!arg) continue;
    if (typeof arg === 'string') classes.push(arg);
    else if (Array.isArray(arg)) classes.push(classnames(...arg));
    else if (typeof arg === 'object') {
      for (const [k, v] of Object.entries(arg)) { if (v) classes.push(k); }
    }
  }
  return classes.filter(Boolean).join(' ');
}

classnames.js

Classnames

mediumcodingJavaScriptStrings

Overview

Implement classnames(...args) that joins class names. Supports strings, objects (keys with truthy values), and arrays.

Examples

classnames('foo', { bar: true, baz: false }, 'qux'); // 'foo bar qux'
classnames('a', ['b', { c: true }]); // 'a b c'

Solution

Reveal solution

function classnames(...args) {
  const classes = [];
  for (const arg of args) {
    if (!arg) continue;
    if (typeof arg === 'string') classes.push(arg);
    else if (Array.isArray(arg)) classes.push(classnames(...arg));
    else if (typeof arg === 'object') {
      for (const [k, v] of Object.entries(arg)) { if (v) classes.push(k); }
    }
  }
  return classes.filter(Boolean).join(' ');
}

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