js如何判斷小數 JS判斷只能是數字和小數點

轉載：http://www.cnblogs.com/zangdalei/p/4732548.html#undefined

js如何判斷小數點後有幾位

<script>  
  var   n=3.143423423;
alert(n.toString().split(".")[1].length);  
  </script> 
js javascrip 截取小數點後幾位

第一種，利用math.round 

   var original=28.453
1) //round "original" to two decimals
var result=Math.round(original*100)/100;  //returns 28.45
2) // round "original" to 1 decimal
var result=Math.round(original*10)/10;  //returns 28.5

 

第二種，js1.5以上能夠利用toFixed(x) ，可指定數字截取小數點後 x位

3) //round "original" to two decimals
var result=original.toFixed(2); //returns 28.45

4) // round "original" to 1 decimal
var result=original.toFixed(1); //returns 28.5

 

以上兩種方法最通用，但卻沒法知足某些特殊要求，好比保留小數點後兩位，若是不滿兩位，不滿兩位則補零。此時就有了第三種方法

[javascript]  view plain copy

 

 

function roundNumber(number,decimals) {
    var newString;// The new rounded number
    decimals = Number(decimals);
    if (decimals < 1) {
        newString = (Math.round(number)).toString();
    } else {
        var numString = number.toString();
        if (numString.lastIndexOf(".") == -1) {// If there is no decimal point
            numString += ".";// give it one at the end
        }
        var cutoff = numString.lastIndexOf(".") + decimals;// The point at which to truncate the number
        var d1 = Number(numString.substring(cutoff,cutoff+1));// The value of the last decimal place that we'll end up with
        var d2 = Number(numString.substring(cutoff+1,cutoff+2));// The next decimal, after the last one we want
        if (d2 >= 5) {// Do we need to round up at all? If not, the string will just be truncated
            if (d1 == 9 && cutoff > 0) {// If the last digit is 9, find a new cutoff point
                while (cutoff > 0 && (d1 == 9 || isNaN(d1))) {
                    if (d1 != ".") {
                        cutoff -= 1;
                        d1 = Number(numString.substring(cutoff,cutoff+1));
                    } else {
                        cutoff -= 1;
                    }
                }
            }
            d1 += 1;
        }
        if (d1 == 10) {
            numString = numString.substring(0, numString.lastIndexOf("."));
            var roundedNum = Number(numString) + 1;
            newString = roundedNum.toString() + '.';
        } else {
            newString = numString.substring(0,cutoff) + d1.toString();
        }
    }
    if (newString.lastIndexOf(".") == -1) {// Do this again, to the new string
        newString += ".";
    }
    var decs = (newString.substring(newString.lastIndexOf(".")+1)).length;
    for(var i=0;i<decimals-decs;i++) newString += "0";

JS判斷只能是數字和小數點

1.文本框只能輸入數字代碼(小數點也不能輸入) 
<input onkeyup="this.value=this.value.replace(/\D/g,'')" onafterpaste="this.value=this.value.replace(/\D/g,'')"> 

2.只能輸入數字,能輸小數點. 
<input onkeyup="if(isNaN(value))execCommand('undo')" onafterpaste="if(isNaN(value))execCommand('undo')"> 
<input name=txt1 onchange="if(/\D/.test(this.value)){alert('只能輸入數字');this.value='';}"> 

3.數字和小數點方法二 
<input type=text tvalue="" ovalue="" onkeypress="if(!this.value.match(/^[\+\-]?\d*?\.?\d*?$/))this.value=this.t_value;else this.tvalue=this.value;if(this.value.match(/^(?:[\+\-]?\d+(?:\.\d+)?)?$/))this.ovalue=this.value" onkeyup="if(!this.value.match(/^[\+\-]?\d*?\.?\d*?$/))this.value=this.t_value;else this.tvalue=this.value;if(this.value.match(/^(?:[\+\-]?\d+(?:\.\d+)?)?$/))this.ovalue=this.value" onblur="if(!this.value.match(/^(?:[\+\-]?\d+(?:\.\d+)?|\.\d*?)?$/))this.value=this.o_value;else{if(this.value.match(/^\.\d+$/))this.value=0+this.value;if(this.value.match(/^\.$/))this.value=0;this.ovalue=this.value}">

4.只能輸入字母和漢字 
<input onkeyup="value=value.replace(/[\d]/g,'') "onbeforepaste="clipboardData.setData('text',clipboardData.getData('text').replace(/[\d]/g,''))" maxlength=10 name="Numbers"> 

5.只能輸入英文字母和數字,不能輸入中文 
<input onkeyup="value=value.replace(/[^\w\.\/]/ig,'')"> 

6.只能輸入數字和英文<font color="Red">chun</font> 
<input onKeyUp="value=value.replace(/[^\d|chun]/g,'')"> 

7.小數點後只能有最多兩位(數字,中文均可輸入),不能輸入字母和運算符號: 
<input onKeyPress="if((event.keyCode<48 || event.keyCode>57) && event.keyCode!=46 || /\.\d\d$/.test(value))event.returnValue=false"> 

8.小數點後只能有最多兩位(數字,字母,中文均可輸入),能夠輸入運算符號: 
<input onkeyup="this.value=this.value.replace(/^(\-)*(\d+)\.(\d\d).*$/,'$1$2.$3')"> 

 

jquery 四捨五入截取字符串

JS 方法：<script type="text/javascript">// 獲得字符串的真實長度（雙字節換算爲兩個單字節）function getStrActualLen(sChars){    //sChars.replace(/[^\x00-\xff]/g,"xx").length/1024+"字節"; //Math.round(sChars.replace(/[^\x00-\xff]/g,"xx").length/1024);這個貌似很差使 return alert(formatNum(sChars.replace(/[^\x00-\xff]/g,"xx").length/1024,4));}//格式化小數，並四捨五入。如：formatNum(100.12345678,4) function formatNum(Num1,Num2){      if(isNaN(Num1)||isNaN(Num2)){            return(0);      }else{            Num1=Num1.toString();            Num2=parseInt(Num2);            if(Num1.indexOf('.')==-1){                  return(Num1);            }else{                  var b=Num1.substring(0,Num1.indexOf('.')+Num2+1);                  var c=Num1.substring(Num1.indexOf('.')+Num2+1,Num1.indexOf('.')+Num2+2);                  if(c==""){                        return(b);                  }else{                        if(parseInt(c)<5){                              return(b);                        }else{                              return((Math.round(parseFloat(b)*Math.pow(10,Num2))+Math.round(parseFloat(Math.pow(0.1,Num2).toString().substring(0,Math.pow(0.1,Num2).toString().indexOf('.')+Num2+1))*Math.pow(10,Num2)))/Math.pow(10,Num2));                        }                  }            }      } } Jquery方法：function getStrActualLen(){var count=$("#sChars").val().length/1024; return Math.round(count*Math.pow(10,4));}