我如何检查一个变量的类型是否为布尔类型?
我的意思是，有一些替代方案，比如:
if(jQuery.type(new Boolean()) === jQuery.type(variable))
//Do something..
但这对我来说不太好。
有没有更清洁的方式来实现这个目标?
当前回答
基准:
都很相似……
const { performance } = require('perf_hooks');
const boolyah = true;
var t0 = 0;
var t1 = 0;
const loops = 1000000;
var results = { 1: 0, 2: 0, 3: 0, 4: 0 };
for (i = 0; i < loops; i++) {
t0 = performance.now();
boolyah === false || boolyah === true;
t1 = performance.now();
results['1'] += t1 - t0;
t0 = performance.now();
'boolean' === typeof boolyah;
t1 = performance.now();
results['2'] += t1 - t0;
t0 = performance.now();
!!boolyah === boolyah;
t1 = performance.now();
results['3'] += t1 - t0;
t0 = performance.now();
Boolean(boolyah) === boolyah;
t1 = performance.now();
results['4'] += t1 - t0;
}
console.log(results);
// RESULTS
// '0': 135.09559339284897,
// '1': 136.38034391403198,
// '2': 136.29421120882034,
// '3': 135.1228678226471,
// '4': 135.11531442403793
其他回答
基准:
都很相似……
const { performance } = require('perf_hooks');
const boolyah = true;
var t0 = 0;
var t1 = 0;
const loops = 1000000;
var results = { 1: 0, 2: 0, 3: 0, 4: 0 };
for (i = 0; i < loops; i++) {
t0 = performance.now();
boolyah === false || boolyah === true;
t1 = performance.now();
results['1'] += t1 - t0;
t0 = performance.now();
'boolean' === typeof boolyah;
t1 = performance.now();
results['2'] += t1 - t0;
t0 = performance.now();
!!boolyah === boolyah;
t1 = performance.now();
results['3'] += t1 - t0;
t0 = performance.now();
Boolean(boolyah) === boolyah;
t1 = performance.now();
results['4'] += t1 - t0;
}
console.log(results);
// RESULTS
// '0': 135.09559339284897,
// '1': 136.38034391403198,
// '2': 136.29421120882034,
// '3': 135.1228678226471,
// '4': 135.11531442403793
关于es2015箭头函数的另一个决策
const isBoolean = val => typeof val === 'boolean';
在JavaScript中检查变量类型最可靠的方法是:
var toType = function(obj) {
return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase()
}
toType(new Boolean(true)) // returns "boolean"
toType(true); // returns "boolean"
造成这种复杂性的原因是typeof true返回“boolean”，而typeof new boolean (true)返回“object”。
判断真假最简单的方法是: (typeof value === "boolean")， 但如果value是布尔类的实例，则返回"object"。因此，为了处理这个问题，我们必须添加另一个条件来检查是否: (value instanceof Boolean)
代码片段:
const value = false;
//const value = new Boolean(10);
//const value = new Boolean("hi");
if((typeof value === "boolean") || (value instanceof Boolean))
console.log("boolean");
else
console.log("not boolean");
这就是typeof存在的意义。括号是可选的，因为它是一个操作符。
if (typeof variable == "boolean") {
// variable is a boolean
}
