Javascript Regexp replace multiple strings matching property names of another object literal

Question

I have these declared:

var obj = {aaa: "came", bbb: "saw", ccc: "conquered", zzz: "discarded" };

var str = "I {aaa}, I {bbb}, I {ccc}. Then I {aaa} again."

What I want to do is str.replace() each curly braced string with the appropriately named property from obj. So in the end, I should have:

I came, I saw, I conquered. Then I came again.

Thank you.

EDIT: The linked duplicate indeed proved very appropriate for my case. In addition, answers on that question actually provide dynamic solutions for the case where I did not know the properties of obj ahead of time.

Possible duplicate of How to replace string {} value to obj (key value) — RomanPerekhrest
– RomanPerekhrest, Commented Jun 15, 2019 at 8:26
Downvoter, in case it's due to the duplicate flag, please forgive ;) I actually searched SO a whole lot before going ahead to post a new question. Perhaps that answer didn't come up high on the list because the title has no "RegExp" and no "Javascript"! — Ifedi Okonkwo
– Ifedi Okonkwo, Commented Jun 15, 2019 at 8:52

CertainPerformance · Accepted Answer · 2019-06-15 08:24:36Z

4

Capture what comes between {}s, and use a callback for the replacer to look up that captured property on the object:

var obj = {aaa: "came", bbb: "saw", ccc: "conquered", zzz: "discarded" };
var str = "I {aaa}, I {bbb}, I {ccc}. Then I {aaa} again.";

const output = str.replace(/{([^}]+)}/g, (_, prop) => obj[prop]);
console.log(output);

answered Jun 15, 2019 at 8:24

CertainPerformance

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5 Comments

kemicofa Over a year ago

Hey, could you explain how the regex captures everything between {}? How does [^}]+ capture all characters? What is specifically the point of ^} ? Thanks

kemicofa Over a year ago

@Andreas thanks for the link. Though I'm still confused how [^}] represents "Match a single character not present in the list below". Why is it not ?

CertainPerformance Over a year ago

@kemicofa It matches "one or more characters which are not }". So the whole pattern means "match {, repeatedly match anything but }, then match }". You could also use {(.*?)}, but that's less efficient

Andreas Over a year ago

@kemicofa [...] match any character in the list, [^...] match anything that is not (^) in the list

kemicofa Over a year ago

@Andreas ahh ok. I was thinking of ^ as in first element. Thanks.

Code Maniac · Accepted Answer · 2019-06-15 08:28:41Z

3

You can use callback function of replace method

var obj = {aaa: "came", bbb: "saw", ccc: "conquered", zzz: "discarded" };
var str = "I {aaa}, I {bbb}, I {ccc}. Then I {aaa} again."

let op = str.replace(/\{([^}]+)\}/g, (_,g1)=> obj[g1] || _)

console.log(op)

answered Jun 15, 2019 at 8:28

Code Maniac

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1 Comment

Ifedi Okonkwo Over a year ago

Great and elegant! Absolutely new syntax to me. Thank you.

Prasad Telkikar · Accepted Answer · 2019-06-15 08:26:37Z

2

Easiest and elegant approach is to use string interpolation

var obj = {aaa: "came", bbb: "saw", ccc: "conquered", zzz: "discarded" };

var str = `I ${obj.aaa}, I ${obj.bbb}, I ${obj.ccc}. Then I ${obj.aaa} again.`

console.log(str);

answered Jun 15, 2019 at 8:26

Prasad Telkikar

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1 Comment

Ifedi Okonkwo Over a year ago

Thank you sir. However, this solution would require knowing each and every object property name ahead of time.

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