freeCodeCamp/part-042.md at 6ccd0d21a1ab40d2a7ce6d5a3a4ca1bd4d86387f

Randell Dawson b9c9a95223 chore(learn): Renamed all project-based curriculum project step filenames to use 3-digit format of part-ddd.md (#39463 )

* fix: renamed basic html cat photo app steps

* fix: renamed css-variables project steps

* fix: renamed d3-dashboard filenames

* fix: renamed rpg-game filenames

* fix: renamed functional-progamming-spreadsheet filenames

* fix: renamed calorie-counter project filenames

2020-09-16 11:54:12 +05:30

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id, title, challengeType, isHidden

id	title	challengeType	isHidden
5d7925341747ad42b12f8e68	Part 42	0	true

Description

This is still valid because we're modifying arr in place instead of reassigning to it (which is invalid with the const keyword). But doing this still modifies state, and we don't want to do that in functional programming.

The concat method returns a new array instead of modifying an existing one:

[1,2,3].concat(4); // [1, 2, 3, 4]
[1,2,3].concat(4, 5); // [1, 2, 3, 4, 5]

Use concat instead of push to return the result of adding end to arr.

Instructions

Tests

tests:
  - text: See description above for instructions.
    testString: assert(JSON.stringify(range(1,2)) === "[1,2]" && code.includes("concat") && !(code.includes("push")));

Challenge Seed

<script>

const infixToFunction = {
  "+": (x, y) => x + y,
  "-": (x, y) => x - y,
  "*": (x, y) => x * y,
  "/": (x, y) => x / y
};

const infixEval = (str, regex) =>
  str.replace(regex, (_, arg1, fn, arg2) =>
    infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
  );

const highPrecedence = str => {
  const regex = /([0-9.]+)([*\/])([0-9.]+)/;
  const str2 = infixEval(str, regex);
  return str === str2 ? str : highPrecedence(str2);
};

const spreadsheetFunctions = {
  "": x => x
};

const applyFn = str => {
  const noHigh = highPrecedence(str);
  const infix = /([0-9.]+)([+-])([0-9.]+)/;
  const str2 = infixEval(noHigh, infix);
  const regex = /([a-z]*)\(([0-9., ]*)\)(?!.*\()/i;
  const toNumberList = args => args.split(",").map(parseFloat);
  const applyFunction = (fn, args) =>
    spreadsheetFunctions[fn.toLowerCase()](toNumberList(args));
  return str2.replace(
    regex,
    (match, fn, args) =>
      spreadsheetFunctions.hasOwnProperty(fn.toLowerCase()) ? applyFunction(fn, args) : match
  );
};

const range = (start, end) => {
  const arr = [start];
  arr.push(end);
  return arr;
}


</script>

Before Test

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Spreadsheet</title>
  <style>
    #container {
      display: grid;
      grid-template-columns: 50px repeat(10, 200px);
      grid-template-rows: repeat(11, 30px);
    }
    .label {
      background-color: lightgray;
      text-align: center;
      vertical-align: middle;
      line-height: 30px;
    }
  </style>
</head>
<body>
<div id="container">
  <div></div>
</div>

After Test

</body>
</html>

Solution

<script>
const infixToFunction = {
  "+": (x, y) => x + y,
  "-": (x, y) => x - y,
  "*": (x, y) => x * y,
  "/": (x, y) => x / y
};

const infixEval = (str, regex) =>
  str.replace(regex, (_, arg1, fn, arg2) =>
    infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
  );

const highPrecedence = str => {
  const regex = /([0-9.]+)([*\/])([0-9.]+)/;
  const str2 = infixEval(str, regex);
  return str === str2 ? str : highPrecedence(str2);
};

const spreadsheetFunctions = {
  "": x => x
};

const applyFn = str => {
  const noHigh = highPrecedence(str);
  const infix = /([0-9.]+)([+-])([0-9.]+)/;
  const str2 = infixEval(noHigh, infix);
  const regex = /([a-z]*)\(([0-9., ]*)\)(?!.*\()/i;
  const toNumberList = args => args.split(",").map(parseFloat);
  const applyFunction = (fn, args) =>
    spreadsheetFunctions[fn.toLowerCase()](toNumberList(args));
  return str2.replace(
    regex,
    (match, fn, args) =>
      spreadsheetFunctions.hasOwnProperty(fn.toLowerCase()) ? applyFunction(fn, args) : match
  );
};

const range = (start, end) => {
  const arr = [start];
  return arr.concat(end);
}
</script>

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