为什么 JavaScript 函数调用中没有 () {parantheses}
Why there is not () {parantheses} in JavaScript function calling
这是 index.js 文件的代码快照,它是在新的 phonegap 项目中默认创建的。
var app = {
// Application Constructor
initialize: function() {
this.bindEvents();
},
// Bind Event Listeners
//
// Bind any events that are required on startup. Common events are:
// 'load', 'deviceready', 'offline', and 'online'.
bindEvents: function() {
document.addEventListener('deviceready', this.onDeviceReady, false);
},
// deviceready Event Handler
//
// The scope of 'this' is the event. In order to call the 'receivedEvent'
// function, we must explicitly call 'app.receivedEvent(...);'
onDeviceReady: function() {
app.receivedEvent('deviceready');
},
// Update DOM on a Received Event
receivedEvent: function(id) {
var parentElement = document.getElementById(id);
var listeningElement = parentElement.querySelector('.listening');
var receivedElement = parentElement.querySelector('.received');
listeningElement.setAttribute('style', 'display:none;');
receivedElement.setAttribute('style', 'display:block;');
console.log('Received Event: ' + id);
}
};
第 11 行,
document.addEventListener('deviceready', this.onDeviceReady, false);
我假设 this.onDeviceReady
是一个函数调用,那么为什么这里没有像 this.onDeviceReady()
这样的 ()
?
this.onDeviceReady
是这里的函数引用。在函数上使用 ()
时,会立即调用。
当使用函数引用时,函数被传递给另一个函数,当某些事件发生时,函数被调用。
这与
相同
function somefun(callback) {
// When something ASYNCHRONOUS process completes, call the callback function
callback();
}
var myFun = function() {
console.log('in myFun');
};
function somefun(myFun);
如果我们在将函数作为引用传递时将 () 与 this.onDeviceReady
一起使用,将立即调用 onDeviceReady() 方法。
这是 index.js 文件的代码快照,它是在新的 phonegap 项目中默认创建的。
var app = {
// Application Constructor
initialize: function() {
this.bindEvents();
},
// Bind Event Listeners
//
// Bind any events that are required on startup. Common events are:
// 'load', 'deviceready', 'offline', and 'online'.
bindEvents: function() {
document.addEventListener('deviceready', this.onDeviceReady, false);
},
// deviceready Event Handler
//
// The scope of 'this' is the event. In order to call the 'receivedEvent'
// function, we must explicitly call 'app.receivedEvent(...);'
onDeviceReady: function() {
app.receivedEvent('deviceready');
},
// Update DOM on a Received Event
receivedEvent: function(id) {
var parentElement = document.getElementById(id);
var listeningElement = parentElement.querySelector('.listening');
var receivedElement = parentElement.querySelector('.received');
listeningElement.setAttribute('style', 'display:none;');
receivedElement.setAttribute('style', 'display:block;');
console.log('Received Event: ' + id);
}
};
第 11 行,
document.addEventListener('deviceready', this.onDeviceReady, false);
我假设 this.onDeviceReady
是一个函数调用,那么为什么这里没有像 this.onDeviceReady()
这样的 ()
?
this.onDeviceReady
是这里的函数引用。在函数上使用 ()
时,会立即调用。
当使用函数引用时,函数被传递给另一个函数,当某些事件发生时,函数被调用。
这与
相同function somefun(callback) {
// When something ASYNCHRONOUS process completes, call the callback function
callback();
}
var myFun = function() {
console.log('in myFun');
};
function somefun(myFun);
如果我们在将函数作为引用传递时将 () 与 this.onDeviceReady
一起使用,将立即调用 onDeviceReady() 方法。