Javascript - RegEx Uppercase and LowerCase and Mixed

Question

I have this code:

var cadena = prompt("Cadena:"); document.write(mayusminus(cadena)); function mayusminus(cad){ var resultado = "Desconocido"; if(cad.match(new RegExp("[A-Z]"))){ resultado="mayúsculas"; }else{ if(cad.match(new RegExp("[a-z]"))){ resultado="minúsculas"; }else{ if(cad.match(new RegExp("[a-zA-z]"))){ resultado = "minúsculas y MAYUSCULAS"; } } } return resultado; }

I always have mayusculas or minusculas, never minusculas y MAYUSCULAS (MIXED), I am learning regexp and dont know my error yet :S

Please add the call of mayusminus to your question, including its parameters, the expected result and the actual result. — Zeta
– Zeta, Commented Oct 5, 2012 at 12:08
you have a mistake in the last [a-zA-z] - it should be [a-zA-Z] in any case (pun intended) — mplungjan
– mplungjan, Commented Oct 5, 2012 at 12:18
Zeta you can read all the post and you see the call to mayusminus, and the expected result and actual result :S — Genaut
– Genaut, Commented Oct 5, 2012 at 14:00

Mike Samuel · Accepted Answer · 2012-10-05 12:10:52Z

new RegExp("[A-Z]")

matches when any character in cadena is an upper-case letter. To match when all characters are upper-case, use

new RegExp("^[A-Z]+$")

The ^ forces it to start at the start, the $ forces it to end at the end and the + ensures that between the end there are one or more of [A-Z].

Ωmega · Accepted Answer · 2012-10-05 12:27:30Z

I believe you wanted to use regex patterns ^[a-z]+$, ^[A-Z]+$ and ^[a-zA-Z]+$.

In regex, the caret ^ matches the position before the first character in the string. Similarly, $ matches right after the last character in the string. Additionaly, + means one or more occurrences.

It is necessary to use ^ and $ in the pattern, if you want to ensure no other then listed characters are in the string.

JavaScript:

s = 'tEst'; r = (s.match(new RegExp("^[a-z]+$"))) ? 'minúsculas' : (s.match(new RegExp("^[A-Z]+$"))) ? 'mayúsculas' : (s.match(new RegExp("^[a-zA-Z]+$"))) ? 'minúsculas y mayúsculas' : 'desconocido';

Test this code here.

sp00m · Accepted Answer · 2012-10-05 12:28:02Z

Let's say cad is foo:

// will return false if (cad.match(new RegExp("[A-Z]"))) { resultado="mayúsculas"; // so will go there } else { // will return true if (cad.match(new RegExp("[a-z]"))) { // so will go there resultado="minúsculas"; } else { if (cad.match(new RegExp("[a-zA-z]"))) { resultado = "minúsculas y MAYUSCULAS"; } } }

Now, let's say cad is FOO:

// will return true if (cad.match(new RegExp("[A-Z]"))) { // so will go there resultado="mayúsculas"; } else { if (cad.match(new RegExp("[a-z]"))) { resultado="minúsculas"; } else { if (cad.match(new RegExp("[a-zA-z]"))) { resultado = "minúsculas y MAYUSCULAS"; } } }

Finally, let's say cad is FoO:

// will return true if (cad.match(new RegExp("[A-Z]"))) { // so will go there resultado="mayúsculas"; } else { if (cad.match(new RegExp("[a-z]"))) { resultado="minúsculas"; } else { if(cad.match(new RegExp("[a-zA-z]"))) { resultado = "minúsculas y MAYUSCULAS"; } } }

As you can see, the nested else is never visited.

What you can do is:

if (cad.match(new RegExp("^[A-Z]+$"))) { resultado="mayúsculas"; } else if (cad.match(new RegExp("^[a-z]+$"))) { resultado="minúsculas"; } else { resultado = "minúsculas y MAYUSCULAS"; }

Explanation:

^ means from the beginning of the string,

$ means to the end of the string,

<anything>+ means at least one anything.

That said,

^[A-Z]+$ means the string should only contains uppercased chars,

^[a-z]+$ means the string should only contains lowercased chars.

So if the string isn't only composed by uppercased or lowercased chars, the string contains both of them.

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