Substitution of object element string notation with object element value using replace

Question

The following code tries (in a single replace call) to substitute an object element string notation with an object element value using regexp replace.

But only errors are observed in this approach (refer logs below).

The sample code tries to replace the string <> with the object element obj.aa

var obj = {};
obj.aa = '1';
obj.bb = '21';
console.log('<<obj.aa>>'.replace(/<<obj\.(.*)>>/,obj['$1']));
console.log('<<obj.aa>>'.replace(/<<obj\.(.*)>>/,`obj[$1]`));
console.log('<<obj.aa>>'.replace(/<<obj\.(.*)>>/,`${obj[$1]}`));

Log is shown below:

undefined
obj[aa]

console.log('<<obj.aa>>'.replace(/<<obj\.(.*)>>/,`${obj[$1]}`));
                                                    ^

ReferenceError: $1 is not defined
    at Object.<anonymous> (source_file.js:6:57)
    at Module._compile (module.js:410:26)
    at Object.Module._extensions..js (module.js:417:10)
    at Module.load (module.js:344:32)
    at Function.Module._load (module.js:301:12)
    at Function.Module.runMain (module.js:442:10)
    at startup (node.js:136:18)
    at node.js:966:3

Is there any workaround / correct way to achieve this in a replace call line?

Paul · Accepted Answer · 2018-02-21 06:01:39Z

1

You need to use a function for this:

console.log('<<obj.aa>>'.replace(/<<obj\.(.*)>>/, (_,prop) => obj[prop]));

answered Feb 21, 2018 at 6:01

Paul

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