How to reverse an array of characters in place in JavaScript

JavaScript, algorithms, arrays, strings

Here is one way to reverse a string or an array of characters in place in JavaScript.
Space complexity: O(1)
Time complexity: O(n)

Note: In JavaScript, strings are immutable so we are using an array of characters to represent our string.

reverseStringTry in REPL
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// since strings are immutable
// the param 'string' will be represented as an array of characters
function reverse(string) {
    if (string === null) return null
    if (string.length === 1) return string;
    // iterate until midpoint of string and swap ends
    for (let i = 0; i < Math.floor((string.length-1)/2); i++) {
        const front = i;
        const back = string.length-1-i;
        swap(string, front, back);
    }
    return string;
}
function swap(array, i, j) {
    const temp = array[i];
    array[i] = array[j]
    array[j] = temp;
}
// ==== Tests
function runTests(func) {
  const inputOutput = [[null, null], [[''], ['']], [['f','o','o',' ', 'b', 'a', 'r'], ['r', 'a', 'b', ' ', 'o', 'o', 'f']]];
  
  for (let i = 0; i < inputOutput.length; i++) {
    const input = inputOutput[i].slice(0, inputOutput[i].length-1);
  
    const expected = inputOutput[i][inputOutput[i].length-1];
    const result = func(...input);
    
    if (!deepEquals(result, expected)) {
      return `Test failed: Expected - ${expected}. Got ${result}`;
    }
  }
  return 'All tests passed!'
}
runTests(reverse); // All tests passed
// Test cases
// reverse(null); // null
// reverse(['']); // ''
// reverse(['f','o','o',' ','b','a','r']) // '['r', 'a', 'b', ' ', 'o', 'o', 'f']'
// ==== Test helpers
function deepEquals(x, y) {
  if ((typeof x === "object" && x !== null) && (typeof y === "object" && y !== null)) {
    if (Object.keys(x).length != Object.keys(y).length)
      return false;
    for (var prop in x) {
      if (y.hasOwnProperty(prop))
      {  
        if (!deepEquals(x[prop], y[prop]))
          return false;
      }
      else
        return false;
    }
    return true;
  }
  else if (x !== y)
    return false;
  else
    return true;
}
runTests(reverse); // All tests passed