Java Basic Learning Experience 03

Function

• The Name property of the function returns the names of the functions;
• toStringthe use of a multi-line string can be implemented in disguise:

var multiline = function (fn) {  var arr = fn.toString().split(‘\n’);  return arr.slice(1, arr.length - 1).join(‘\n’);};function f() {/*  这是一个  多行注释*/}multiline(f);// “ 这是一个//   多行注释”

• Note that for the var command, local variables can only be declared inside the function, declared in other chunks, and all are global variables;
• The scope at which the function executes is the scope at which it was defined, not the scope at which it was called:

var a = 1;var x = function () {  console.log(a);};function f() {  var a = 2;  x();}f() // 1//很容易犯错的一点是，如果函数A调用函数B，却没考虑到函数B不会引用函数A的内部变量。var B = function () {  console.log(a);};function A(f) {  var a = 2;  f();}A(B)// ReferenceError: a is not defined

• The runtime does not give an error, no matter how many parameters are supplied (or if no parameters are supplied). The value of the omitted parameter becomes undefined;
• The length property of a function is independent of the number of arguments actually passed in, reflecting only the number of arguments the function expects to pass in.
• Return cannot be used alone and must be used in a function;
• The most common scenario for Eval is to parse the JSON data string, but the correct approach should be to use the native Json.parse method;

Strict mode andevalWith

1. The external scope code cannot get eval the variables defined inside:

(function f() {  ‘use strict’;  eval(‘var foo = 123’);  console.log(foo);  // ReferenceError: foo is not defined})()

1. But eval the values of variables that can read and write to the external scope:

(function f() {  ‘use strict’;  var foo = 1;  eval(‘foo = 2’);  console.log(foo);  // 2})()

• In order to ensure that eval aliases do not affect code optimization, JAVASCRIPT standards stipulate that all aliases eval are performed with eval an internal global scope:

//下面这些形式都是eval的别名调用，作用域都是全局作用域。eval.call(null, ‘…’)window.eval(‘…’)(1, eval)(‘…’)(eval, eval)(‘…’)

Java Basic Learning experience