尝试锻炼如何处理数组

Question

I'm in the process of teaching myself javascript and it looks at though I've hit a road block. As an exercise I am trying to build a tax calculator.

Here is an object I built that contains the tax brackets:

var taxBracket = [
{bracket: 1, from:0, to:18200, percentage :0, amount:0},
{bracket: 2, from:18201, to:37000, percentage :19, over:18200, amount:0},
{bracket: 3, from:37001, to:80000, percentage :32.5, over:37000, amount:3752},
{bracket: 4, from:80001, to:180000, percentage :37, over:80000, amount:17547},
{bracket: 5, from:180001, to:0, percentage :45, over:180000, amount:54547}];

and here is the function that loops through object to find the corresponding tax bracket of y

function returnTax (y){
    for(var x in taxBracket){
    if (y >= taxBracket[x].from && y <= taxBracket[x].to){
        var z = taxBracket[x].amount + ((grossIncome-taxBracket[x].over) * (taxBracket[x].percentage/100));
        return z;   
    }
};

The issue is that if y is over 180000, it errors out as to is 0. Is this only solution to this an else statement repeating the functions of the if statement? Thank for your help!

Answer 1

Good job with it so far. Simply using Infinity instead of defaulting to 0 on the final bracket will fix it. I've made a couple of recommendations on your syntax as well, hope it helps.

var taxBracket = [
    {bracket: 1, from: 0, to: 18200, percentage: 0, amount: 0},
    {bracket: 2, from: 18201, to: 37000, percentage: 19, over: 18200, amount: 0},
    {bracket: 3, from: 37001, to: 80000, percentage: 32.5, over: 37000, amount: 3752},
    {bracket: 4, from: 80001, to: 180000, percentage: 37, over: 80000, amount: 17547},

    // Use Infinity instead of 0 for the "to" value of bracket 5
    {bracket: 5, from: 180001, to: Infinity, percentage: 45, over: 180000, amount: 54547}
];

// Variable names like 'x', 'y' and 'z' can cause problems with code readability.
// Descriptive names such as "income", or even "string" or "int" will help you out when you come to review your code later!
function returnTax(y){

    // Using for..in with arrays can cause issues with enumerating over object properties.
    // You don't have to worry about it in this case, but a standard for loop (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for) is better practice.
    for(var x = 0; x < taxBracket.length; x++){

        if(y <= taxBracket[x].to){

            // I find breaking up long calculations into separate variables can make it
            // more readable. More preference than anything else though!
            var amountOver = grossIncome - taxBracket[x].over;
            var percent = taxBracket[x].percentage / 100;
            return taxBracket[x].amount + (amountOver * percent);

        }

    }

}

Answer 2

You are creating an array literal of object literals. You should loop through arrays with a standard for loop.

Answer 3

一种解决方案是使最后一个“ to”字段的数量非常大。

Answer 4

you can use built in function to loop array of object like

yourArray.forEach
( function (arrayItem)
{
var x =
arrayItem.prop1 + 2;
alert(x);
 });