Why is √ is not allowed as a objectName/stringName/functionName/NumberName?

Question

I am coding a scientific calculator and I need some help:

function √(in){
    return Math.sqrt();
}
// throws an error
var √ = function(in){
    return Math.sqrt();
}
// also throws an error

var √ = "sqrt";
√randomSqNum = 100,
√random = {sqrt:4,cubert:8},
√sqNum = ["0","1","4","9","16","25"],
√null = null,
√undefined = undefined;

They all throw an error! Please explain why they throw an error. Also, Is there a way around this?

In what charset/encoding is your code? It should be Unicode (UTF-8), otherwise such var/func names are illegal — hindmost, Sep 10 '15 at 16:06

score 5 · Answer 1 · edited Sep 10 '15 at 18:10

5

In Javascript, variable names must begin with a letter, _ or $. More information here:

http://www.w3schools.com/js/js_variables.asp

edited Sep 10 '15 at 18:10

Pavel Gatnar

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answered Sep 10 '15 at 16:11

MHardwick

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If so, then explain why I could set a function/object/string/number named π without any errors? – Joseph Goh Sep 10 '15 at 16:14
2

https://mathiasbynens.be/notes/javascript-identifiers-es6 – epascarello Sep 10 '15 at 16:15
3

@JosephGoh π is a letter – Pointy Sep 10 '15 at 16:16
Exactly what they said. π is a greek letter, and in this particular language is treated as a valid variable/function start letter, while the square root symbol isn't a letter in any language. – MHardwick Sep 10 '15 at 16:18
Just updated my question* @MHardwick – Joseph Goh Sep 10 '15 at 16:27

Pavel Gatnar · Answer 2 · 2015-09-10T18:57:12.057

3

You cannot use it directly as a name, but you can use it as key.

var f={}
f["√"] = Math.sqrt
alert(f["√"](5))

In such way you can define +-*/ and many other funcions.

f["+"] = function(a){
  return a.reduce(function(p,v){
    return p+v
  },0)
}

And when you have a parsed statement tree in form {o:fn,a:[s1,...,sn]} where fn is function name and s1,...,sn are subtrees or values, then you can simply get the result:

function calc(st){
  return (typeof st == 'object')?f[st.o].apply(null,st.a.map(calc)):st
}

edited Sep 10 '15 at 18:57

answered Sep 10 '15 at 16:24

Pavel Gatnar

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Thanks for the answer! – Joseph Goh Sep 10 '15 at 16:28

Felix Kling · Accepted Answer · 2015-09-10T16:53:51.647

3

JavaScript follows annex 31 of the unicode standard regarding identifier names.

I assume you are using U+221A as character. As you can see from the linked page, it can neither be used at the beginning of an identifier nor within it:

(likely because it is not even a letter).

Compare that to π, which is a letter and which can be used in an identifier name.

Also, Is there a way around this?

No. However, you can always try to find letters that look similar.

edited Sep 10 '15 at 16:53

answered Sep 10 '15 at 16:27

Felix Kling

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Really helpful, Thanks for taking your time to write this answer. – Joseph Goh Sep 10 '15 at 16:53

Why is √ is not allowed as a objectName/stringName/functionName/NumberName?

3 Answers3