如何发现一个数字是浮点数或整数？
1.25 --> float
1 --> integer
0 --> integer
0.25 --> float
当前回答
为什么不这样做：
var isInt = function(n) { return parseInt(n) === n };
其他回答
在这里尝试了一些答案，我最终写出了这个解决方案。这也适用于字符串中的数字。
function isInt(number) {
if(!/^["|']{0,1}[-]{0,1}\d{0,}(\.{0,1}\d+)["|']{0,1}$/.test(number)) return false;
return !(number - parseInt(number));
}
function isFloat(number) {
if(!/^["|']{0,1}[-]{0,1}\d{0,}(\.{0,1}\d+)["|']{0,1}$/.test(number)) return false;
return number - parseInt(number) ? true : false;
}
var测试={“integer”：1，“浮动”：1.1，“整数InString”：“5”，“floatInString”：“5.5”，“负Int”：-345，“负浮动”：-34.98，“negativeIntString”：“-45”，“negativeFloatString”：“-23.09”，“notValidFalse”：false，“notValidTrue”：true，“notValidString”：“45lorem”，“notValidStringFloat”：“4.5lorem”，'notValidNan'：NaN，“notValidObj”：｛｝，“notValidArr”：[1,2]，};函数isInt（数字）{如果（！/^[“|']｛0,1｝[-]｛0.1｝\d｛0，｝（\.｛0,1｝\d+）[“|']｛0 1｝$/.test（数字））返回false；回来（number-parseInt（number））；}函数isFloat（数字）{如果（！/^[“|']｛0,1｝[-]｛0.1｝\d｛0，｝（\.｛0,1｝\d+）[“|']｛0 1｝$/.test（数字））返回false；返回number-parseInt（number）？真：假；}函数测试函数（obj）{var keys=对象.keys（obj）；var values=对象.值（obj）；values.forEach（函数（元素，索引）{console.log（`${keys[index]}（${element}）var是整数吗$｛isInt（元素）｝`）；console.log（`${keys[index]}（${element}）var是浮点数吗$｛isFloat（元素）｝`）；});}testFunctions（测试）；
下面的函数防止空字符串、未定义、空值和max/min值范围。Javascript引擎从一开始就应该内置这些函数。：）
享受
function IsInteger(iVal) {
var iParsedVal; //our internal converted int value
iParsedVal = parseInt(iVal,10);
if (isNaN(iParsedVal) || Infinity == iParsedVal || -Infinity == iParsedVal) //sanity check - guard against empty strings and max/min values
return false;
else
return Number(iVal) === (iParsedVal | 0); //the 2nd operand group (intValue | 0), evaluates to true only if the intValue is an integer; so an int type will only return true
}
function IsFloat(fVal) {
var fParsedVal; //our internal converted float value
fParsedVal = parseFloat(fVal);
if (isNaN(fParsedVal) || Infinity == fParsedVal || -Infinity == fParsedVal) //sanity check - guard against empty strings and max/min values
return false;
else
return !!(fVal % 1); //true only if there is a fractional value after the mod op; the !! returns the opposite value of the op which reflects the function's return value
}
我喜欢这个小函数，它对正整数和负整数都会返回true：
function isInt(val) {
return ["string","number"].indexOf(typeof(val)) > -1 && val !== '' && !isNaN(val+".0");
}
这之所以有效，是因为1或“1”变为“1.0”，isNaN（）返回false（然后我们对其进行否定并返回），但1.0或“1.0”变成“1.0.0”，而“string”变成“string.0”，两者都不是数字，所以isNaN）返回false，（并且再次被否定）。
如果你只想要正整数，有一个变体：
function isPositiveInt(val) {
return ["string","number"].indexOf(typeof(val)) > -1 && val !== '' && !isNaN("0"+val);
}
或者，对于负整数：
function isNegativeInt(val) {
return `["string","number"].indexOf(typeof(val)) > -1` && val !== '' && isNaN("0"+val);
}
isPositiveInt（）通过将连接的数字字符串移到要测试的值之前来工作。例如，isPositiveInt（1）导致isNaN（）求值为“01”，结果为false。同时，isPositiveInt（-1）导致isNaN（）求值为“0-1”，结果为true。我们否定了返回值，这给了我们想要的。isNegativeInt（）的工作原理类似，但不否定isNaN（）的返回值。
编辑：
我的原始实现也会在数组和空字符串上返回true。这个实现没有这个缺陷。如果val不是字符串或数字，或者如果它是空字符串，那么它还具有提前返回的优点，这在这些情况下会更快。您可以通过将前两个子句替换为
typeof(val) != "number"
如果您只想匹配文字数字（而不是字符串）
编辑：
我还不能发表评论，所以我在回答中添加了这个。@Asok发布的基准信息非常丰富；然而，最快的函数不符合要求，因为它还为浮点数、数组、布尔值和空字符串返回TRUE。
我创建了以下测试套件来测试每个函数，并将我的答案添加到列表中（函数8解析字符串，函数9解析字符串）：
funcs = [
function(n) {
return n % 1 == 0;
},
function(n) {
return typeof n === 'number' && n % 1 == 0;
},
function(n) {
return typeof n === 'number' && parseFloat(n) == parseInt(n, 10) && !isNaN(n);
},
function(n) {
return n.toString().indexOf('.') === -1;
},
function(n) {
return n === +n && n === (n|0);
},
function(n) {
return parseInt(n) === n;
},
function(n) {
return /^-?[0-9]+$/.test(n.toString());
},
function(n) {
if ((undefined === n) || (null === n)) {
return false;
}
if (typeof n == 'number') {
return true;
}
return !isNaN(n - 0);
},
function(n) {
return ["string","number"].indexOf(typeof(n)) > -1 && n !== '' && !isNaN(n+".0");
}
];
vals = [
[1,true],
[-1,true],
[1.1,false],
[-1.1,false],
[[],false],
[{},false],
[true,false],
[false,false],
[null,false],
["",false],
["a",false],
["1",null],
["-1",null],
["1.1",null],
["-1.1",null]
];
for (var i in funcs) {
var pass = true;
console.log("Testing function "+i);
for (var ii in vals) {
var n = vals[ii][0];
var ns;
if (n === null) {
ns = n+"";
} else {
switch (typeof(n)) {
case "string":
ns = "'" + n + "'";
break;
case "object":
ns = Object.prototype.toString.call(n);
break;
default:
ns = n;
}
ns = "("+typeof(n)+") "+ns;
}
var x = vals[ii][1];
var xs;
if (x === null) {
xs = "(ANY)";
} else {
switch (typeof(x)) {
case "string":
xs = "'" + n + "'";
break;
case "object":
xs = Object.prototype.toString.call(x);
break;
default:
xs = x;
}
xs = "("+typeof(x)+") "+xs;
}
var rms;
try {
var r = funcs[i](n);
var rs;
if (r === null) {
rs = r+"";
} else {
switch (typeof(r)) {
case "string":
rs = "'" + r + "'";
break;
case "object":
rs = Object.prototype.toString.call(r);
break;
default:
rs = r;
}
rs = "("+typeof(r)+") "+rs;
}
var m;
var ms;
if (x === null) {
m = true;
ms = "N/A";
} else if (typeof(x) == 'object') {
m = (xs === rs);
ms = m;
} else {
m = (x === r);
ms = m;
}
if (!m) {
pass = false;
}
rms = "Result: "+rs+", Match: "+ms;
} catch (e) {
rms = "Test skipped; function threw exception!"
}
console.log(" Value: "+ns+", Expect: "+xs+", "+rms);
}
console.log(pass ? "PASS!" : "FAIL!");
}
我还重新运行了基准测试，将函数#8添加到列表中。我不会发布结果，因为它们有点尴尬（例如，函数不快）。。。
（删节——我删除了成功的测试，因为输出很长）结果如下：
Testing function 0
Value: (object) [object Array], Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) true, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) false, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: null, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) '', Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) '1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
FAIL!
Testing function 1
Value: (string) '1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 2
Value: (string) '1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 3
Value: (object) true, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (object) false, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) [object Array], Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) [object Object], Expect: (boolean) false, Result: (boolean) true, Match: false
Value: null, Expect: (boolean) false, Test skipped; function threw exception!
Value: (string) '', Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) 'a', Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) '1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
FAIL!
Testing function 4
Value: (string) '1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 5
Value: (string) '1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 6
Value: null, Expect: (boolean) false, Test skipped; function threw exception!
Value: (string) '1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 7
Value: (number) 1.1, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (number) -1.1, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (object) true, Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) [object Array], Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (boolean) [object Object], Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) '', Expect: (boolean) false, Result: (boolean) true, Match: false
Value: (string) '1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) true, Match: N/A
FAIL!
Testing function 8
Value: (string) '1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) true, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
Testing function 9
Value: (string) '1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
Value: (string) '-1.1', Expect: (ANY), Result: (boolean) false, Match: N/A
PASS!
我留下了失败，这样你就可以看到每个函数在哪里失败，（string）“#”测试，这样你就能看到每个函数是如何处理字符串中的整数和浮点值的，因为有些人可能希望这些值被解析为数字，有些人可能不希望。
在测试的10个功能中，实际符合OP要求的是[1,3,5,6,8,9]
YourJS提供了以下两个函数，这些函数适用于所有数字，包括为Infinity和Infinity返回false：
function isFloat(x) {
return typeOf(x, 'Number') && !!(x % 1);
}
function isInt(x) {
return typeOf(x, 'Number') && x % 1 == 0;
}
由于typeOf（）是一个YourJS内部函数，如果你想使用这些定义，你可以在这里下载这些函数的版本：http://yourjs.com/snippets/build/34
当除以1时检查余数：
function isInt(n) {
return n % 1 === 0;
}
如果你不知道参数是一个数字，你需要两个测试：
function isInt(n){
return Number(n) === n && n % 1 === 0;
}
function isFloat(n){
return Number(n) === n && n % 1 !== 0;
}
2019年更新在这个答案写出来5年后，一个解决方案在ECMA脚本2015中被标准化。这个答案涵盖了这个解决方案。
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