检查字符串是否以标点符号开头（Javascript）

Question

How can I check if my data string begins with a punctuation mark using Javascript? I looked at Check if string is a punctuation character and How to know that a string starts/ends with a specific string in jQuery? and a number of others, but I can't tell where I'm going wrong.

Here's a snippet of what I have so far:

      var punctuations = [".", ",", ":", "!", "?"];

      if (d.endContext.startsWith(punctuations)) {console.log(d.endContext)
      } else {console.log('false')};

I only get 'false' returns, but if I pass in "." in

if(d.endContext.startsWith('.'))
... 

I get correct results. I also tried

     String punctuations = ".,:;?!"

like Check if string is a punctuation character suggested, but both Chrome and Firefox gave me error messages ("Uncaught Syntax Error: Unexpected Identifier" and "SyntaxError: missing ; before statement", respectively). It seemed like that error was usually for writing multiline strings in Javascript, which I don't think I'm trying to do. d.endContext will print multi-line strings, but it works fine when I just pass ".", so I don't think that's the issue.

Answer 1

using Regex is much simpler.

    var str = '.abc'
    var result = !!str.match(/^[.,:!?]/)
    
    console.log(result)

• / indicates start/end of Regular expression

• ^ means 'start with'

• [] means 'character set'. it will match any characters between [ and ]

• !! converts what match returns to a boolean. If it returns a match, it is converted to true . If it returns null , it is converted to false.

Additionally, this app is quite good to learn Regex! http://regexr.com/

Have a nice day! :D

Answer 2

Use the some and startsWith methods.

 punctuations.some(function(character) {
     return string.startsWith(character)
});

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some

The some() method tests whether some element in the array passes the test implemented by the provided function. Or you can also use regex

/[.,:!?]/.test(string.charAt(0))

Answer 3

Here's a beautiful solution:

var punctuations = [".", ",", ":", "!", "?"];
var punkyString = ".hello!";
var nonPunkyString = "hello!";

function isPunkyString(str) {
  return punctuations.indexOf(str[0]) > -1;
}

console.log(punkyString, "is punky:", isPunkyString(punkyString));
console.log(nonPunkyString, "is punky:", isPunkyString(nonPunkyString));

Unit tests!

var punkyStrings = punctuations.map(function (item) {
    return item + " <---<< Punctuations!"
});

var nonPunkyStrings = punctuations.map(function (item, i) {
    return i + " <---<< No punctuations!"
});

punkyStrings.forEach(function (item, i) {
    console.log("Expect", "isPunkyString(\"" + item + "\")", "to be true:", isPunkyString(item));
});

nonPunkyStrings.forEach(function (item, i) {
    console.log("Expect", "isPunkyString(\"" + item + "\")", "to be false:", isPunkyString(item));
});

Why is it beautiful? Because I have used the word punky ! :D Oh and I treat the string as an array. Which is nice!

Has anyone else unit tested their code? :D

Answer 4

Using Array.prototype.indexOf is probably the simplest:

var punctuations = [".", ",", ":", "!", "?"];
var stringToSearch = d.endContext;  // Your string to search
if (punctuations.indexOf(stringToSearch.charAt(0)) !== -1) {
    // Your awesome code goes here
}

It's compatible to IE9 and pretty much all Chrome and Firefox (down to 1.5) versions but if you are using jQuery, you can use inArray for further backwards compatibility.

---

Or... just for fun you could go the other end, be cutting edge, and break all non-beta browsers with the new ES7 Array.prototype.includes :

var punctuations = [".", ",", ":", "!", "?"];
var stringToSearch = d.endContext;  // Your string to search
if (punctuations.includes(stringToSearch.charAt(0))) {
    // Your awesome code goes here
}

Compatible with:

• Chrome 47 (not yet released)
• Firefox 43 (not yet released)