javascript判断是否为数字的方法:1、使用isNaN()函数,语法格式“isNaN(value)”,可以检查其参数value是否为非数字值;2、使用test()函数配合正则表达式来判断;3、利用parseFloat()函数来判断。
本教程操作环境:windows7系统、javascript1.8.5版、Dell G3电脑。
1.使用isNaN()函数
isNaN()的缺点就在于 null、空格以及空串会被按照0来处理
NaN: Not a Number
/** *判断是否是数字 * **/ function isRealNum(val){ // isNaN()函数 把空串 空格 以及NUll 按照0来处理 所以先去除, if(val === "" || val ==null){ return false; } if(!isNaN(val)){ //对于空数组和只有一个数值成员的数组或全是数字组成的字符串,isNaN返回false,例如:'123'、[]、[2]、['123'],isNaN返回false, //所以如果不需要val包含这些特殊情况,则这个判断改写为if(!isNaN(val) && typeof val === 'number' ) return true; } else{ return false; } }
isNaN()函数来判断一个值是数字的最正确的方法就是:
// true:数值型的,false:非数值型 function myIsNaN(value) { return typeof value === 'number' && !isNaN(value); }
isNaN()详解
对于空数组和只有一个数值成员的数组,isNaN
返回false
。
isNaN([]) // false isNaN([123]) // false isNaN(['123']) // false
上面代码之所以返回false
,原因是这些数组能被Number
函数转成数值,请参见《数据类型转换》一章。
因此,使用isNaN之前,最好判断一下数据类型。
function myIsNaN(value) { return typeof value === 'number' && !isNaN(value); }
2.使用正则表达式
(1)、校验只要是数字(包含正负整数,0以及正负浮点数)就返回true
/** * 校验只要是数字(包含正负整数,0以及正负浮点数)就返回true **/ function isNumber(val){ var regPos = /^\d+(\.\d+)?$/; //非负浮点数 var regNeg = /^(-(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*)))$/; //负浮点数 if(regPos.test(val) && regNeg.test(val)){ return true; }else{ return false; } }
(2)、校验正负正数就返回true
/** * 校验正负正数就返回true **/ function isIntNum(val){ var regPos = / ^\d+$/; // 非负整数 var regNeg = /^\-[1-9][0-9]*$/; // 负整数 if(regPos.test(val) && regNeg.test(val)){ return true; }else{ return false; } }
常用正则:
"^\\d+$" //非负整数(正整数 + 0) "^[0-9]*[1-9][0-9]*$" //正整数 "^((-\\d+)|(0+))$" //非正整数(负整数 + 0) "^-[0-9]*[1-9][0-9]*$" //负整数 "^-?\\d+$" //整数 "^\\d+(" //非负浮点数(正浮点数 + 0) "^(([0-9]+\\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\\.[0-9]+)|([0-9]*[1-9][0-9]*))$" //正浮点数 "^((-\\d+(" //非正浮点数(负浮点数 + 0) "^(-(([0-9]+\\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\\.[0-9]+)|([0-9]*[1-9][0-9]*)))$" //负浮点数 "^(-?\\d+)(" //浮点数
3.使用parseFloat()函数
/** * 验证数据 是数字:返回true;不是数字:返回false **/ function Number(val) { if (parseFloat(val).toString() == "NaN") { return false; } else { return true; } } //isNaN(val)不能判断空串或一个空格 //如果是一个空串、空格或null,而isNaN是做为数字0进行处理的,而parseInt与parseFloat是返回一个错误消息,这个isNaN检查不严密而导致的。
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