List of JavaScript arrays with indices

Today I was experimenting with regex in JavaScript and stumbled upon a unique data structure that I had never encountered before: an array with some entries having keys. One method that returns such a data structure is the regex match function. Let's take a look at an example:

    var re = /SESSID=\w+=;/;
    var test = 'SESSID=aaaa=;fjsdfjd';
    var arr = test.match(re);
    console.log(arr);  // ["SESSID=aaaa=;", index: 0, input: "SESSID=aaaa=;fjsdfjd"]
    console.log(arr[0]);  // SESSID=aaaa=;
    console.log(arr['index']);  // 0
    console.log(arr['input']);  // SESSID=aaaa=;fjsdfjd

Can you decipher what's happening here?

javascript

Answer №1

Arrays are essentially objects in disguise, capable of holding a variety of properties.

Although arrays treat numeric string-named properties differently due to the "length" property, they still function like regular object properties.

It's worth mentioning that adding non-numeric properties to an array comes with some caveats. Unlike numeric properties, non-numeric ones won't impact the "length" value and won't be included in the output when using JSON.stringify() on the array.

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