# Learn Functional Programming by Building a Spreadsheet - Step 70

### Tell us what’s happening:

isn’t

``````infixToFunction.operator
``````

and

``````infixToFunction[operator]
``````

the same?

``````<!-- file: index.html -->
<!DOCTYPE html>
<html lang="en">
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<body>
<div id="container">
<div></div>
</div>
<script src="./script.js"></script>
</body>
</html>
``````
``````/* file: styles.css */
#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;
}
``````
``````/* file: script.js */
const infixToFunction = {
"+": (x, y) => x + y,
"-": (x, y) => x - y,
"*": (x, y) => x * y,
"/": (x, y) => x / y,
}

// User Editable Region

const infixEval = (str, regex) => str.replace(regex, (_match, arg1, operator, arg2) => infixToFunction.operator);

// User Editable Region

const isEven = num => num % 2 === 0;
const sum = nums => nums.reduce((acc, el) => acc + el, 0);
const average = nums => sum(nums) / nums.length;

const median = nums => {
const sorted = nums.slice().sort((a, b) => a - b);
const length = sorted.length;
const middle = length / 2 - 1;
return isEven(length)
? average([sorted[middle], sorted[middle + 1]])
: sorted[Math.ceil(middle)];
}

sum,
average,
median
}

const range = (start, end) => Array(end - start + 1).fill(start).map((element, index) => element + index);
const charRange = (start, end) => range(start.charCodeAt(0), end.charCodeAt(0)).map(code => String.fromCharCode(code));

const evalFormula = (x, cells) => {
const idToText = id => cells.find(cell => cell.id === id).value;
const rangeRegex = /([A-J])([1-9][0-9]?):([A-J])([1-9][0-9]?)/gi;
const rangeFromString = (num1, num2) => range(parseInt(num1), parseInt(num2));
const elemValue = num => character => idToText(character + num);
const addCharacters = character1 => character2 => num => charRange(character1, character2).map(elemValue(num));
const rangeExpanded = x.replace(rangeRegex, (_match, char1, num1, char2, num2) => rangeFromString(num1, num2).map(addCharacters(char1)(char2)));
const cellRegex = /[A-J][1-9][0-9]?/gi;
const cellExpanded = rangeExpanded.replace(cellRegex, match => idToText(match.toUpperCase()));
}

const container = document.getElementById("container");
const createLabel = (name) => {
const label = document.createElement("div");
label.className = "label";
label.textContent = name;
container.appendChild(label);
}
const letters = charRange("A", "J");
letters.forEach(createLabel);
range(1, 99).forEach(number => {
createLabel(number);
letters.forEach(letter => {
const input = document.createElement("input");
input.type = "text";
input.id = letter + number;
input.ariaLabel = letter + number;
input.onchange = update;
container.appendChild(input);
})
})
}

const update = event => {
const element = event.target;
const value = element.value.replace(/\s/g, "");
if (!value.includes(element.id) && value.startsWith('=')) {

}
}
``````

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36`

### Challenge Information:

Learn Functional Programming by Building a Spreadsheet - Step 70

no, it’s not the same

here you are accessing a property literally named `operator`, it’s equivalent to `infixToFunction["operator"]`

this one, first the variable inside the square parenthesis is evaluated to the value it contains, then the property is accessed

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