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问题 I am doing an ajax request when an anchor tag is clicked with an ID set to href. Btw, this anchor tag is dynamically created. <a href="983" class="commentDeleteLink">delete</a> When the anchor tag is clicked the following code is executed: $('.commentDeleteLink').live('click', function(event) { event.preventDefault(); var result = confirm('Proceed?'); if ( result ) { $.ajax({ url: window.config.AJAX_REQUEST, type: "POST", data: { action : 'DELCOMMENT', comment : $('#commentText').val(),

问题 I don't understand why but i'm getting this error when I try to initialize the google.maps.Geocoder. Here is the error: Uncaught TypeError: undefined is not a function And the code : function updateMapPosition(map){ var geocoder = new google.maps.Geocoder(); //crashes here !! var position = geocoder.geocode( {'address':$('#id_address').val()}, function(results,status){ if(status == google.maps.GeocoderStatus.OK){ if (status != google.maps.GeocoderStatus.ZERO_RESULTS) { map.setCenter(results[0

问题 Possible Duplicate: Detecting an undefined object property in JavaScript javascript undefined compare How we can add a check for an undefined variable, like: function A(val) { if (val == undefined) // do this else // do this } 回答1: JQuery library was developed specifically to simplify and to unify certain JavaScript functionality. However if you need to check a variable against undefined value, there is no need to invent any special method, since JavaScript has a typeof operator, which is

问题 How to undefine a variable in Scheme? Is this possible? 回答1: In Scheme, variables are defined with either lambda, or one of the various lets. If you want one of them to be 'undefined' then all you need to do is leave the scope that they're in. Of course, that's not really undefining them, it's just that the variable is no longer bound to its previous definition. If you're making top level definitions, using (define), then technically you're defining a function. Since Scheme is functional,

问题 How to undefine a variable in Scheme? Is this possible? 回答1: In Scheme, variables are defined with either lambda, or one of the various lets. If you want one of them to be 'undefined' then all you need to do is leave the scope that they're in. Of course, that's not really undefining them, it's just that the variable is no longer bound to its previous definition. If you're making top level definitions, using (define), then technically you're defining a function. Since Scheme is functional,

问题 In javascript to check if a variable was never created, we just do if (typeof MyVariable !== "undefined"){ ... } I was wonder how I do that in coffeescript?... I try something like if (MyVariable?false){ ... } but this check if MyVariable is a function if so that will call MyVariable(false) if not that will call void(0) or something like that. 回答1: Finally I found this easy way to do it: if (MyVariable?){ ... } that will generate: if (typeof MyVariable !== "undefined" && MyVariable !== null){

问题 I was using console.log() in some JavaScript I wrote and an error of: console is not defined was thrown in Internet Explorer (worked fine in other browsers). I have replaced it with: if (console) console.log("..."); If console is undefined , I would expect the condition to evaluate as false . Ergo, the statement console.log wouldn't be executed and shouldn't throw an error. Instead, an error of: console is not defined at character 4 is thrown. Is this a IE bug? Or is that "if" condition

问题 In PHP, is there any way that I can ignore functions that are undefined instead of throwing a fatal error that is visible in the browser?—i.e., Fatal error: Call to undefined function I know that there is the practice of wrapping all custom functions in a conditional as below, but is there a programmatic way to get this effect? if (function_exists('my_function')) { // use my_function() here; } 回答1: No. Fatal errors are fatal. Even if you were to write your own error handler or use the @ error

问题 I'm checking if(response[0].title !== undefined) , but I get the error: Uncaught TypeError: Cannot read property 'title' of undefined. 回答1: response[0] is not defined, check if it is defined and then check for its property title. if(typeof response[0] !== 'undefined' && typeof response[0].title !== 'undefined'){ //Do something } 回答2: Just check if response[0] is undefined: if(response[0] !== undefined) { ... } If you still need to explicitly check the title, do so after the initial check: if

问题 What exactly is the difference between undefined and void 0 ? Which is preferred and why? 回答1: The difference is that some browsers allow you to overwrite the value of undefined . However, void(anything) always returns real undefined . undefined = 1; console.log(!!undefined); //true console.log(!!void(0)); //false 回答2: undefined has normal variable semantics that not even strict mode can fix and requires run-time look-up. It can be shadowed like any other variable, and the default global