如何在TypeScript中進行數字舍入？

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在本教程中，我們將學習如何在TypeScript中進行數字舍入。在TypeScript中，數字資料型別可以包含帶有小數部分的數值，有時我們需要透過舍入數值來去除小數部分。

例如，如果您想在應用程式中顯示某事物的進度，並且您獲得了進度的十進位制值，但只想顯示整數，則需要對數字進行舍入。

在這裡，我們將學習3到4種不同的舍入數字的方法。

使用Math.round()方法舍入數字

在TypeScript中，Math.round()方法用於將數字舍入到最接近的小數位。它返回舍入數字後的整數值。

語法

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

在上面的語法中，我們建立了數字變數並使用math.round()方法來舍入數字。

引數

Math.round()方法接受一個引數，如下所示。

• number − 需要舍入到最接近整數的數值。

示例

在下面的示例中，我們建立了四個包含不同值的數字變數。之後，我們使用Math.round()方法來舍入每個數值。

在輸出中，使用者可以看到，由於number1的小數部分更接近322而不是323，因此它被向下舍入到322。與number1一樣，number2最接近323，因此它被向上舍入到323。此外，number4變數被舍入到無窮大，因為它的值是無窮大。

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)
);

編譯後，它將生成以下JavaScript程式碼：

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));

輸出

上述程式碼將產生以下輸出：

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()方法向下舍入數字

Math.trunc()方法始終向下舍入作為引數傳遞的數值。我們也可以使用Math.trunc()方法來去除TypeScript中數字的小數部分。

語法

使用者可以按照以下語法學習如何使用Math.trunc()方法向下舍入數字。

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

這裡var1是需要向下舍入的值。

示例

在下面的示例中，我們定義了四個數字並用各種值初始化它們。我們使用Math.trunc()方法向下舍入或去除數字的小數部分。

在輸出中，使用者可以看到var1、var2和var3都被舍入到100，因為該方法去除了小數部分。

// 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));

編譯後，它將生成以下JavaScript程式碼：

// 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));

輸出

上述程式碼將產生以下輸出：

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()方法向上舍入數字

使用者可以按照以下語法使用Math.ceil()方法向上舍入數字。

語法

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

這裡num1是我們想使用Math.ceil()方法向上舍入的數值。

示例

使用者可以看到我們使用了Math.ceil()方法向上舍入數字。在輸出中，我們可以看到num1和num2變數都被向上舍入到100，即使num2非常接近99。由於num3已經是整數，因此它保持不變。

// 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));

編譯後，它將生成以下JavaScript程式碼：

// 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));

輸出

上述程式碼將產生以下輸出：

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()方法將數字舍入到特定小數位

在TypeScript中，我們可以使用toFixed()方法將數字舍入到特定的小數位。例如，如果我們想將數字舍入到五位小數，toFixed()方法將保留小數點後正好五位整數。如果數字的小數點後沒有五位或多於五位整數，它會附加0，但它返回具有精確5位小數位的數字。

語法

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

上面的語法向我們展示瞭如何使用toFixed()方法處理十進位制數字進行舍入。

引數

• decimal_place − 這是您要舍入參考數字的小數位總數。

示例

在下面的示例中，我們使用toFixed()方法處理不同的數值，以舍入到特定的小數位。在輸出中，我們可以看到變數B是如何透過新增零舍入到5位小數的。

// 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)
);

編譯後，它將生成以下JavaScript程式碼：

// 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));

輸出

上述程式碼將產生以下輸出：

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，我們討論了在TypeScript中舍入數字的不同方法。