JavaScript Patterns 4.7 Init-Time Branching
When you know that a certain condition will not change throughout the life of the program, it makes sense to test the condition only once. Browser sniffing (or feature detection) is a typical example.
// BEFORE
var utils = {
addListener : function(el, type, fn) {
if ( typeof window.addEventListener === 'function') {
el.addEventListener(type, fn, false);
} else if ( typeof document.attachEvent === 'function') {// IE
el.attachEvent('on' + type, fn);
} else {// older browsers
el['on' + type] = fn;
}
},
removeListener : function(el, type, fn) {
// pretty much the same...
}
};
// AFTER
// the interface
var utils = {
addListener : null,
removeListener : null
};
// the implementation
if ( typeof window.addEventListener === 'function') {
utils.addListener = function(el, type, fn) {
el.addEventListener(type, fn, false);
};
utils.removeListener = function(el, type, fn) {
el.removeEventListener(type, fn, false);
};
} else if ( typeof document.attachEvent === 'function') {// IE
utils.addListener = function(el, type, fn) {
el.attachEvent('on' + type, fn);
};
utils.removeListener = function(el, type, fn) {
el.detachEvent('on' + type, fn);
};
} else {// older browsers
utils.addListener = function(el, type, fn) {
el['on' + type] = fn;
};
utils.removeListener = function(el, type, fn) {
el['on' + type] = null;
};
}
References:
JavaScript Patterns - by Stoyan Stefanov (O`Reilly)
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