Immutable Strings And Mutable Arrays

Strings in JavaScript are immutable which means that once a string is defined, it cannot be changed anymore. Trying to change a string with a standard String-function will only create a new string and not affect the original string. Consider the following example, where the value in string1 is not changed:

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var string1 = "LOREM IPSUM";
string1.toLowerCase();
console.log(string1);
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Data types in JavaScript

Inspired from an exercise in Hackerrank.com, I found the opportunity to present you the data types that JavaScript defines, which are the following six:

  • undefined
  • null
  • number
  • string
  • boolean
  • object

Arrays and functions are plain objects in JavaScript and they both belong to the object data type.

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Using a variable as a regular expression to find all matches inside a string

Often I have to use a value from a variable and not a fixed string inside a regular expression. For example if I wanted to iterate over the english alphabet and find the number of occurrences of each letter inside a string, I had to do something like the following:

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var testString = "Lorem ipsum dolor sit amet, consetetur sadipscing elitr.";
var matches = testString.match(/a/g).length;
// do this for all the remaining letters

the previous example would work and would find all occurrences of “a”.

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