如果JavaScript字符串以连字符开头，则计算出现次数

Question

Basically I have an array of strings like this:

var array = [
    'Top level',
    '- Sub item',
    '-- Child of sub',
    'Another top',
    'Yet another top',
    '- Child',
];

I'm trying to loop each string and check if the string starts with a hyphen, if so count how many times and then remove.

I can do it kind of like this:

if (string.substring(0, 1) == "-") {
    // ...
} else if (string.substring(0, 2) == "--") {
    // ...
} else if (string.substring(0, 3) == "---") {
    // ...
}

I haven't tested but you can get the idea..

I'm hoping for an easier solution maybe with a regex? Any help?

Thanks.

-- EDIT --

I need to count and remove the hyphens from each string because I have a text area for a user to enter a string with new lines and hyphens.

Textarea value:

Top level
- Sub item
-- Child of sub
Another top
Yet another top
- Child

I am then exploding the textarea value into an array:

var array = textareaValue.split('\n');

for (var i = 0; i < array.length; i++) {
    var this = array[i];
    // Now check for hyphens and count how many
    // if (hyphens === '-')
    // else if (hyphens === '--') ...etc
};

Answer 1

Assuming you're already looping through to get 'string' (I've used 'val' below to remove possible confusion with 'string' type in other languages)

val = val.replace(/^-+/, '')

Edit: tested and there's no need to escape the '-' in this usage

Explanation:

• .replace is a method of all strings
• using // allows a regex
• ^ start of line
• '-' literal
• '+' one or more

Update: to include get the count, you can do:

var matches = val.match("^(-+).*");
length = matches == null ? 0 : matches[1].length;

• match is a method of all strings
• '^' match start
• '(' ')' applies a group, which is returned in the second value of matches, ie the [1]
• ?: used because if there's no match, then matches will be null

Update to match question's edit:

var array = textareaValue.split('\n');

for (var i = 0; i < array.length; i++) {
    var thisValue = array[i];
    // Now check for hyphens and count how many
    var matches = thisValue.match("^(-+).*");
    var hyphenCount = matches == null ? 0 : matches[1].length;
    var fixedValue = thisValue.replace(/^-+/, '')
};

Answer 2

var count = [];
array = array.map(function(str) {
    var match = str.match(/^(-*) ?/);
    count.push(match[1].length);
    return str.substr(match[0].length);
});

Answer 3

You can count matches (ie how many hyphens) with a regular expression , and then replace them using the same RegEx matches.

More info on regular expressions and JavaScript: http://www.w3schools.com/js/js_regexp.asp

Answer 4

You can simply map over the strings, using a regular expression to match (and implicitly count) the hyphens and attaching the remainder of each string.

 var array = [ 'Top level', '- Sub item', '-- Child of sub', 'Another top', 'Yet another top', '- Child', ]; function countCharacter(data, char) { var rex = /^(-*)(.*)$/; // hyphens in first group, body in second return data.map(function(it) { var res = it.match(rex); console.log(res); return { count: res[1].length, text: res[2] }; }); } document.getElementById('r').textContent = JSON.stringify(countCharacter(array, '-')); 

 <pre id=r></pre> 

Answer 5

Yet another variant with map and replace with function

array.map(function(v){
    var s,vv=0;
    s = v.replace(/^-+/,function(p1){
     vv = p1.length;
     return '';
}) 
    return {
        s:s, v:vv
    }
});

 var array = [ 'Top level', '- Sub item', '-- Child of sub', 'Another top', 'Yet another top', '- Child', ]; var mapped = array.map(function(v){ var s,vv=0; s = v.replace(/^-+/,function(p1){ vv = p1.length; return ''; }) return { name:s, count:vv } }); document.getElementById('res').innerHTML = JSON.stringify(mapped, null,2); 

 <pre id='res'></pre> 

Answer 6

Here is how you can get count and replacement in single match invocation :

for (var i = 0; i < array.length; i++) {
    var elem = array[i];
    var m = (elem.match(/^(-+)(.*)$/) || ['', elem]);
    var count = m[1].length;
    var replaced = m[2];
};

If an element doesn't have - at start then above code will get count=0 and replaced same as original string.