What is the default parameter value for function settings in Javascript?

For how to set the default parameter values for functions in Javascript (js), the following methods are provided for reference.

Method 1:

Function example (a, B) {var a = arguments [0]? Arguments [0]: 1; // set the default value of parameter a to 1var B = arguments [1]? Arguments [1]: 2; // set the default value of parameter B to 2 return a + B ;}

Note that the above functions can also be written as follows:

Function example () {var a = arguments [0]? Arguments [0]: 1; // set the default value of the first parameter to 1var B = arguments [1]? Arguments [1]: 2; // set the default value of the second parameter to 2 return a + B ;}

Call example:

Alert (example (); // output 3 alert (example (10); // OUTPUT 12 alert (example (10, 20 )); // output 30 alert (example (null, 20); // output 20

Method 2:

Function example (name, age) {name = name | 'mink xy'; age = age | 21; alert ('Hello! I am '+ name +', and I am '+ age +' years old. ');}

This function can also be written as follows:

Function example (name, age) {if (! Name) {name = 'mink xy';} if (! Age) {age = 21;} alert ('Hello! I am '+ name +', and I am '+ age +' years old. ');}

Call example:

Example ('wang wu'); // output: Hello! I'm Wang Wu, 21 years old. Example ('wang wu', 30); // output: Hello! I'm Wang Wu, 30 years old. Example (null, 30); // output: Hello! I'm a 30-year-old.

The third method is suitable for scenarios with many parameters. Jquery extensions are used:

Function example (setting) {var defaultSetting = {name: 'marchine', age: '30', sex: 'female ', phone: '123', QQ: '123 ', birthday: '2017. 10.01 '}; $. extend (defaultSetting, settings); var message = 'name: '+ defaultSetting. name + ', Gender:' + defaultSetting. sex + ', age:' + defaultSetting. age + ', tel:' + defaultSetting. phone + ', QQ:' + defaultSetting. QQ + ', birthday:' + defaultSetting. birthday + '. '; Alert (message );}

Call example:

Example ({name: 'wang Zhaojun ', sex: 'female', phone: '000000'}); // output: name: Wang Zhaojun, Gender: female, age: 30, tel: 10089, QQ: 10086, birthday: 1949.10.01.

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