regex Return false?

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6

console.log(rule);
// rule = max18
// rule = max120
// rule = max6
var pattMax = new RegExp('^(max).(\d{1,3})');

pattMax.test(rule); //false?

if(pattMax.test(rule)){
    console.log('é max seguido de 1 á 3 digitos');
}
javascript regex

  • To simplify this regex there, you should always marry max1, max12 or max123? will use the groups p something?

  • no, how would it look? but this is not going through and when I test on sites how regexr works.

  • In theory, enough ^max\d{1,3} - the dot would take other characters, like max_121. Max120 would work for the wrong reason, the dot would take 1, and the /d{1,3} would take the 20

3 answers

7

You need to escape the \d or pass the argument i in the regex builder.

var pattMax = new RegExp('^(max)(\d{1,3})', 'i');

pattMax.test(rule); //false?

if(pattMax.test(rule)){
    console.log('é max seguido de 1 á 3 digitos');
}

Based on: javascript new regexp from string

6


You were almost there. You must escape \d for \\d inside the Regexp constructor. Otherwise it is "forgotten". Notice here how the bar disappears:

console.log(new RegExp('^(max).(\d{1,3})'));

If you did the regex like this var pattMax = /'^(max).(\d{1,3})/; your code would almost work:

var pattMax = /^(max).(\d{1,3})/;
['max18', 'max120', 'max6'].forEach(function(rule) {
    console.log(pattMax.test(rule) ? 'é max seguido de 1 á 3 digitos' : 'Falhou!');
});

What fails is that he waits max plus any character except new line (the .) and then numbers in the amount of 1 to 3.

I think you could use it just like this: /^max\d{1,3}/ construction-free:

var pattMax = /^max\d{1,3}/;
['max18', 'max120', 'max6'].forEach(function(rule) {
    console.log(pattMax.test(rule) ? 'é max seguido de 1 á 3 digitos' : 'Falhou!');
});

5

In theory, enough ^max\d{1,3}

The dot in your original Regex takes other characters, like max_121.

Max120 would work for the wrong reason, the point would take the 1, and the /d{1,3} would take the 20.

Describing his query:

^(max).(\d{1,3})
^                 marca decomeço da linha
 (   ) (       )  grupos de retorno
  max             literal "max"
      .           qualquer caractere, mas tem que ter algum
        \d{1,3}   de um a três dígitos

Proposed version

^max\d{1,3}
^                 começo da linha
 max              literal "max"
    \d{1,3}       de um a três digitos

depending on the use, you can omit the ^ (line start), or even add $ end (end of line) if you will operate on larger strings and do not want to accept substrings.

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