在JSON查询中使用变量。

I am trying to write a function that can take a field name as an argument and return an array of corresponding values from a bit of JSON.

我正在尝试编写一个函数，它可以将字段名作为参数，并从JSON中返回相应的值数组。

Example object:

例对象:

var myObject = [
   {"x": 10, "y": 10},
   {"x": 20, "y": 10},
   {"x": 20, "y": 20},
   {"x": 10, "y": 20}
];

My function looks something like this:

我的函数是这样的

function getValues(desiredValue) {
   var values = [];
   for (i = 0; i < myObject.length; i++) {
      values[i] = myObject[i].desiredValue;
   }
   return values;
}
getValues(x);

Ideally, I would have the argument x passed to the getValues which, instead of looking for a field name called desiredValue would look for a field name called x.

理想情况下，我将参数x传递给getValues，而不是寻找一个名为desiredValue的字段名，而是寻找一个名为x的字段名。

The returned array should look like this:

返回的数组应该如下所示:

[10,20,20,10]

As the problem with this code is obvious, how can I get the desired result?

由于这段代码的问题很明显，我如何才能得到期望的结果?

Also, I am trying to avoid unnecessary dependencies, so please don’t give me any JQuery unless absolutely necessary.

另外，我正在尽量避免不必要的依赖，所以请不要给我任何JQuery，除非绝对必要。

4 个解决方案

#1

You can use map() to return desired result.

可以使用map()返回所需的结果。

var myObject = [
   {"x": 10, "y": 10},
   {"x": 20, "y": 10},
   {"x": 20, "y": 20},
   {"x": 10, "y": 20}
];

function getValues(desiredValue) {
  return myObject.map(e => e[desiredValue]);
}

console.log(getValues('x'))

#2

You actually need to parse the given JSON string (not the array that you have given here) by using JSON.parse(). See: http://jsbin.com/kevoqe/edit?js,console

实际上，您需要使用JSON.parse()解析给定的JSON字符串(不是这里给出的数组)。见:http://jsbin.com/kevoqe/edit?js控制台

#3

a simple utility

一个简单的工具

//also accepts a path like "foo.bar.baz"
//returns undefined if path can't be resolved
function fetch(path){
    var keys = path.split(".");
    return function( target ){
        for(var t = target, i = 0; i < keys.length; t = t[ keys[ i++ ] ])
            if(t == null) return void 0;
        return t;
    }
}

and it's usage

它的使用

var myObject = [
    {"x": 10, "y": 10},
    {"x": 20, "y": 10},
    {"x": 20, "y": 20},
    {"x": 10, "y": 20}
];

var result = myObject.map( fetch("y") );

this version is a bit more flexible than one hardwired with Array.map() because it can easily be composed with other functions.

这个版本比使用Array.map()硬连接的版本灵活一些，因为它可以与其他函数轻松组合。

Although, especially in this particular case, this already is a little bit of overkill. here you can easily write:

虽然，特别是在这个特例中，这已经有点过分了。在这里你可以很容易地写:

var result = myObject.map(pt => pt.y);

you can't get any shorter and simpler. Or if for some reason the property really is dynamic, you'll have some variable containing it:

你不能变得更短更简单。或者如果由于某种原因这个属性是动态的，你会有一些变量包含它:

var dynamicPropertyName = "y";
//...
var result = myObject.map(pt => pt[ dynamicPropertyName ]);

#4

Use array map method to do manipulation in an array of objects.

使用数组映射方法对对象数组进行操作。

Try this code :

试试这段代码:

var myObject = [
   {"x": 10, "y": 10},
   {"x": 20, "y": 10},
   {"x": 20, "y": 20},
   {"x": 10, "y": 20}
];

var output = getValues("x");
console.log(output);

function getValues(desiredValue) {
  return myObject.map(function(item) {
      return item[desiredValue];   
  });
}

Output :

输出:

Working fiddle : https://jsfiddle.net/ffyjyzjb/

工作小提琴:https://jsfiddle.net/ffyjyzjb/

#1