break

break 陳述句會中斷目前的迭代、switch 或 label 陳述句,並將程式流程轉到被中斷之陳述句後的陳述句。

嘗試一下

let i = 0;
while (i < 6) {
 if (i === 3) {
 break;
 }
 i = i + 1;
}
console.log(i);
// Expected output: 3

語法

break [label];

label

可選的。欲中斷陳述句的標籤 (label) 識別。若不是要中斷迭代或 switch,則需加此參數。

說明

中斷陳述 break 可加上標籤 (label) 參數,使其跳出被標籤的陳述語句。此中斷陳述 break 必須被包含在被標籤的陳述語句中。被標籤的陳述語句可被添加於任一個區塊 (block) 前,而非限定在迴圈陳述。

範例

下面函式包含一個中斷陳述 break ,當 i 值為 3 時,中斷 while 迴圈,並回傳 3 * x 。

function testBreak(x) {
 var i = 0;
 while (i < 6) {
 if (i == 3) {
 break;
 }
 i += 1;
 }
 return i * x;
}

The following code uses break statements with labeled blocks. A break statement must be nested within any label it references. Notice that inner_block is nested within outer_block.

outer_block: {
 inner_block: {
 console.log("1");
 break outer_block; // breaks out of both inner_block and outer_block
 console.log(":-("); // skipped
 }
 console.log("2"); // skipped
}

The following code also uses break statements with labeled blocks but generates a Syntax Error because its break statement is within block_1 but references block_2. A break statement must always be nested within any label it references.

block_1: {
 console.log('1');
 break block_2; // SyntaxError: label not found
}
block_2: {
 console.log('2');
}

規範

瀏覽器相容性

參見

• continue
• label
• switch