将Will的评论复制到一个答案中，因为我发现它很有用:

var string = "this is a string";
var length = 20;
var trimmedString = string.length > length ? 
                    string.substring(0, length - 3) + "..." : 
                    string;

谢谢。

和一个jsfiddle为任何人谁关心https://jsfiddle.net/t354gw7e/:)

为什么不直接使用substring…字符串。substring(0、7);第一个参数(0)是起点。第二个参数(7)是结束点(独占)。更多信息请点击这里。

var string = "this is a string";
var length = 7;
var trimmedString = string.substring(0, length);

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/String/substr

从链接:

string.substr(start[, length])

    let trimString = function (string, length) {
      return string.length > length ? 
             string.substring(0, length) + '...' :
             string;
    };

用例,

let string = 'How to trim a string to N chars in Javascript';

trimString(string, 20);

//How to trim a string...

有几种方法可以做到这一点

let description = "your test description your test description your test description";
let finalDesc = shortMe(description, length);

function finalDesc(str, length){

// return str.slice(0,length);

// return str.substr(0, length);

// return str.substring(0, length);

}

您还可以修改此函数以进入字符串之间。

首选String.prototype.slice而不是String.prototype.substring方法(在substring中，在某些情况下它给出的结果与您期望的结果不同)。

从左到右修剪字符串:

const str = "123456789";
result = str.slice(0,5);     // "12345", extracts first 5 characters
result = str.substring(0,5); // "12345"

startIndex > endIndex:

result = str.slice(5,0);     // "", empty string
result = str.substring(5,0); // "12345" , swaps start & end indexes => str.substring(0,5)

从右到左修剪字符串:(-ve start index)

result = str.slice(-3);                 // "789", extracts last 3 characters
result = str.substring(-3);             // "123456789" , -ve becomes 0 => str.substring(0)
result = str.substring(str.length - 3); // "789"