A brief analysis of whether there can be a comma after the last element when assigning values ​​to C/C++, Java, PHP, JavaScript, Json arrays and objects_javascript skills

1 C, C++, Java, and PHP all tolerate trailing commas

When assigning values ​​to arrays in C, C++, and Java, the comma at the end of the last element is optional. The following two lines of code are equivalent for these languages.

int a[] = {1,2,3}; /* 正确 */
int a[] = {1,2,3,}; /* 正确 */

PHP also inherits the characteristics of C. The following two lines of code are equivalent.

$a = array(1,2,3); /* 正确 */
$a = array(1,2,3,); /* 正确 */

2 JavaScript treats the trailing comma as a syntax error!

However, when it comes to JavaScript, the situation is very different. There must be no comma at the end of the last element, otherwise it will be a syntax error.

var a = new Array(1,2,3); //正确
var a = new Array(1,2,3,); //报错

For objects, there cannot be a trailing comma.

var o = { name:'赵', age:12 }; // 正确
var o = { name:'赵', age:12,}; // 报错

Although some browsers are most tolerant after detecting this error, this is not a uniform behavior. IE series browsers cannot tolerate this kind of error.

3 JSON also cannot tolerate trailing commas

{"name":"zhao", "age":12} // 正确的JSON格式
{"name":"zhao", "age":12,} // 错误的JSON格式

It should be noted that JSON is a universal data format and has nothing to do with specific programming languages. Various languages ​​also use different tolerance levels when decoding JSON. PHP's json_decode() does not tolerate trailing commas.

json_decode({"name":"zhao", "age":12,}); // 解析会发生错误

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