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---
id: 5d7925341747ad42b12f8e68
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title: Part 42
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challengeType: 0
---
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# --description--
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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.
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The `concat` method returns a new array instead of modifying an existing one:
```js
[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` .
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# --hints--
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See description above for instructions.
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```js
assert(
JSON.stringify(range(1, 2)) === '[1,2]' & &
code.includes('concat') & &
!code.includes('push')
);
```
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# --seed--
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## --before-user-code--
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```html
<!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 >
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```
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## --after-user-code--
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```html
< / body >
< / html >
```
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## --seed-contents--
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```html
< 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 >
```
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# --solutions--
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```html
< 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 >
```
