JS判断元素为数字的奇异写法分享

var each = _.each = _.forEach = function(obj, iterator, context) {
if (obj == null) return;
if (nativeForEach && obj.forEach === nativeForEach) {
obj.forEach(iterator, context);
} else if (obj.length === +obj.length) {
for (var i = 0, l = obj.length; i < l; i++) {
if (iterator.call(context, obj[i], i, obj) === breaker) return;
}
} else {
for (var key in obj) {
if (_.has(obj, key)) {
if (iterator.call(context, obj[key], key, obj) === breaker) return;
}
}
}
};

if (obj.length === +obj.length)

if (typeof obj.length === 'number')

function isNumber1(a){
return typeof a === 'number'
}

function isNumber2(a) {
return Object.prototype.toString.call(a) === '[object Number]'
}

function isNumber3(a){
return a === +a
}

var arr = ['1', true, false, undefined, null, {}, [], 1]
for (var i=0; i<arr.length; i++) {
console.log(isNumber3(arr[i]))
}