Javascript 在对象中添加到数组时避免if..else梯形图
是否有办法避免以下代码中出现的Javascript 在对象中添加到数组时避免if..else梯形图,javascript,Javascript,是否有办法避免以下代码中出现的if..else情况,并在一行中执行此操作 var myObject = {}, data = ["Chennai", "Thoothukkudi", "Madurai", "Coimbatore", "Trichy", "Salem", "Tirunelveli", "Erode", "Vellore", "Tiruppur"]; data.forEach(function(currentCity) {
if..else
情况,并在一行中执行此操作
var myObject = {},
data = ["Chennai", "Thoothukkudi", "Madurai",
"Coimbatore", "Trichy", "Salem", "Tirunelveli",
"Erode", "Vellore", "Tiruppur"];
data.forEach(function(currentCity) {
if (currentCity[0] in myObject) {
myObject[currentCity[0]].push(currentCity);
} else {
myObject[currentCity[0]] = [currentCity];
}
});
console.log(myObject);
输出
{ C: [ 'Chennai', 'Coimbatore' ],
T: [ 'Thoothukkudi', 'Trichy', 'Tirunelveli', 'Tiruppur' ],
M: [ 'Madurai' ],
S: [ 'Salem' ],
E: [ 'Erode' ],
V: [ 'Vellore' ] }
问题是,我必须这样做,if..else
检查代码中的许多地方。如果我在8个地方这样做,那么总共有40行。所以,我正在寻找一种方法,将其写在一行中
在Python中,有一种称为defaultdict
的东西,普通dict也可以与setdefault
函数一起使用。有什么优雅而简短(行数较少)的方法可以做到这一点吗?像这样:
myObject[currentCity[0]] = myObject[currentCity[0]] || [];
myObject[currentCity[0]].push(currentCity);
像这样:
myObject[currentCity[0]] = myObject[currentCity[0]] || [];
myObject[currentCity[0]].push(currentCity);
您可以将这些行添加到单独的函数中,然后在每个实例中只需调用一次:
function wrangleCity(currentCity, myObject) {
if (currentCity[0] in myObject) {
myObject[currentCity[0]].push(currentCity);
} else {
myObject[currentCity[0]] = [currentCity];
}
}
data.forEach(function (currentCity) {
wrangleCity(currentCity, myObject);
});
您可以将这些行添加到单独的函数中,然后在每个实例中只需调用一次:
function wrangleCity(currentCity, myObject) {
if (currentCity[0] in myObject) {
myObject[currentCity[0]].push(currentCity);
} else {
myObject[currentCity[0]] = [currentCity];
}
}
data.forEach(function (currentCity) {
wrangleCity(currentCity, myObject);
});
与Array.Prototype.forEach比较Array.Prototype.map
利用返回值并实际返回相同大小的新数组
与Array.Prototype.forEach比较
Array.Prototype.map
利用返回值并实际返回一个相同大小的新数组。不应被要求@?编写一个可重用的命名函数。您可以使用三元运算符@thefourtheye不应被要求@?编写一个可重用的命名函数。您可以使用三元运算符@thefourtheye