如何在TypeScript中进行数字舍入？

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在本教程中，我们将学习如何在TypeScript中进行数字舍入。在TypeScript中，数字数据类型可以包含带有小数部分的数值，有时我们需要通过舍入数值来去除小数部分。

例如，如果您想在应用程序中显示某事物的进度，并且您获得了进度的十进制值，但只想显示整数，则需要对数字进行舍入。

在这里，我们将学习3到4种不同的舍入数字的方法。

使用Math.round()方法舍入数字

在TypeScript中，Math.round()方法用于将数字舍入到最接近的小数位。它返回舍入数字后的整数值。

语法

let number1: number = 322.3232;
Math.round(number)

在上面的语法中，我们创建了数字变量并使用math.round()方法来舍入数字。

参数

Math.round()方法接受一个参数，如下所示。

• number − 需要舍入到最接近整数的数值。

示例

在下面的示例中，我们创建了四个包含不同值的数字变量。之后，我们使用Math.round()方法来舍入每个数值。

在输出中，用户可以看到，由于number1的小数部分更接近322而不是323，因此它被向下舍入到322。与number1一样，number2最接近323，因此它被向上舍入到323。此外，number4变量被舍入到无穷大，因为它的值是无穷大。

let number1: number = 322.3232; // number with decimal part near to zero
let number2: number = 0.0300012; // number between 0 and 1
let number3: number = 322.98878; // number with decimal part near to one
let number4: number = Infinity; // infinity value
// Using the Math.round() method for the different number values
console.log(
   "After rounding the " + number1 + " it's value is " + Math.round(number1)
);
console.log(
   "After rounding the " + number2 + " it's value is " + Math.round(number2)
);
console.log(
   "After rounding the " + number3 + " it's value is " + Math.round(number3)
);
console.log(
   "After rounding the " + number4 + " it's value is " + Math.round(number4)
);

编译后，它将生成以下JavaScript代码：

var number1 = 322.3232; // number with decimal part near to zero
var number2 = 0.0300012; // number between 0 and 1
var number3 = 322.98878; // number with decimal part near to one
var number4 = Infinity; // infinity value
// Using the Math.round() method for the different number values
console.log("After rounding the " + number1 + " it's value is " + Math.round(number1));
console.log("After rounding the " + number2 + " it's value is " + Math.round(number2));
console.log("After rounding the " + number3 + " it's value is " + Math.round(number3));
console.log("After rounding the " + number4 + " it's value is " + Math.round(number4));

输出

上述代码将产生以下输出：

After rounding the 322.3232 it's value is 322
After rounding the 0.0300012 it's value is 0
After rounding the 322.98878 it's value is 323
After rounding the Infinity it's value is Infinity

使用Math.trunc()方法向下舍入数字

Math.trunc()方法始终向下舍入作为参数传递的数值。我们也可以使用Math.trunc()方法来去除TypeScript中数字的小数部分。

语法

用户可以按照以下语法学习如何使用Math.trunc()方法向下舍入数字。

let var1: number = 100;
Math.trunc(var1)

这里var1是需要向下舍入的值。

示例

在下面的示例中，我们定义了四个数字并用各种值初始化它们。我们使用Math.trunc()方法向下舍入或去除数字的小数部分。

在输出中，用户可以看到var1、var2和var3都被舍入到100，因为该方法去除了小数部分。

// number variables with the different values
let var1: number = 100;
let var2: number = 100.9999;
let var3: number = 100.0001;
let var4: number = 0.0001;

// using the Math.truc() method to round down the numbers
console.log("After rounding down the " + var1 + " is " + Math.trunc(var1));
console.log("After rounding down the " + var2 + " is " + Math.trunc(var2));
console.log("After rounding down the " + var3 + " is " + Math.trunc(var3));
console.log("After rounding down the " + var4 + " is " + Math.trunc(var4));

编译后，它将生成以下JavaScript代码：

// number variables with the different values
var var1 = 100;
var var2 = 100.9999;
var var3 = 100.0001;
var var4 = 0.0001;

// using the Math.truc() method to round down the numbers
console.log("After rounding down the " + var1 + " is " + Math.trunc(var1));
console.log("After rounding down the " + var2 + " is " + Math.trunc(var2));
console.log("After rounding down the " + var3 + " is " + Math.trunc(var3));
console.log("After rounding down the " + var4 + " is " + Math.trunc(var4));

输出

上述代码将产生以下输出：

After rounding down the 100 is 100
After rounding down the 100.9999 is 100
After rounding down the 100.0001 is 100
After rounding down the 0.0001 is 0

使用Math.ceil()方法向上舍入数字

用户可以按照以下语法使用Math.ceil()方法向上舍入数字。

语法

let num1: number = 99.99;
Math.ceil(num1)

这里num1是我们想使用Math.ceil()方法向上舍入的数值。

示例

用户可以看到我们使用了Math.ceil()方法向上舍入数字。在输出中，我们可以看到num1和num2变量都被向上舍入到100，即使num2非常接近99。由于num3已经是整数，因此它保持不变。

// Defining the various numbers
let num1: number = 99.99; // number near to 100
let num2: number = 99.000001; // number near to 99
let num3: number = 99; // integer value
let num4: number = -Infinity; // infinity value

// Using the Math.ceil() method to round up the numbers
console.log("After rounding up the " + num1 + " is " + Math.ceil(num1));
console.log("After rounding up the " + num2 + " is " + Math.ceil(num2));
console.log("After rounding up the " + num3 + " is " + Math.ceil(num3));
console.log("After rounding up the " + num4 + " is " + Math.ceil(num4));

编译后，它将生成以下JavaScript代码：

// Defining the various numbers
var num1 = 99.99; // number near to 100
var num2 = 99.000001; // number near to 99
var num3 = 99; // integer value
var num4 = -Infinity; // infinity value

// Using the Math.ceil() method to round up the numbers
console.log("After rounding up the " + num1 + " is " + Math.ceil(num1));
console.log("After rounding up the " + num2 + " is " + Math.ceil(num2));
console.log("After rounding up the " + num3 + " is " + Math.ceil(num3));
console.log("After rounding up the " + num4 + " is " + Math.ceil(num4));

输出

上述代码将产生以下输出：

After rounding up the 99.99 is 100
After rounding up the 99.000001 is 100
After rounding up the 99 is 99
After rounding up the -Infinity is -Infinity

使用toFixed()方法将数字舍入到特定小数位

在TypeScript中，我们可以使用toFixed()方法将数字舍入到特定的小数位。例如，如果我们想将数字舍入到五位小数，toFixed()方法将保留小数点后正好五位整数。如果数字的小数点后没有五位或多于五位整数，它会附加0，但它返回具有精确5位小数位的数字。

语法

let variableA: number = 765.656566565565;
variableA.toFixed(decimal_place)

上面的语法向我们展示了如何使用toFixed()方法处理十进制数字进行舍入。

参数

• decimal_place − 这是您要舍入参考数字的小数位总数。

示例

在下面的示例中，我们使用toFixed()方法处理不同的数值，以舍入到特定的小数位。在输出中，我们可以看到变量B是如何通过添加零舍入到5位小数的。

// Different variables with different number of decimal place values
let variableA: number = 765.656566565565;
let variableB: number = 765.2;
let variableC: number = 765;

// Using the toFixed() method to round number to particular decimal place
console.log(
   "After rounding the " +
   variableA +
   " to 3 decimal place is " +
   variableA.toFixed(3)
);
console.log(
   "After rounding the " +
   variableB +
   " to 3 decimal place is " +
   variableB.toFixed(5)
);
console.log(
   "After rounding the " +
   variableC +
   " to 3 decimal place is " +
   variableC.toFixed(0)
);

编译后，它将生成以下JavaScript代码：

// Different variables with different number of decimal place values
var variableA = 765.656566565565;
var variableB = 765.2;
var variableC = 765;

// Using the toFixed() method to round number to particular decimal place
console.log("After rounding the " +
variableA +
" to 3 decimal place is " +
variableA.toFixed(3));
console.log("After rounding the " +
variableB +
" to 3 decimal place is " +
variableB.toFixed(5));
console.log("After rounding the " +
variableC +
" to 3 decimal place is " +
variableC.toFixed(0));

输出

上述代码将产生以下输出：

After rounding the 765.656566565565 to 3 decimal place is 765.657
After rounding the 765.2 to 3 decimal place is 765.20000
After rounding the 765 to 3 decimal place is 765

在本教程中，我们讨论了在TypeScript中舍入数字的不同方法。