Javascript – Call javascript function from asp.net code behind after server side code executes

asp.netjavascript

I have an asp.net button, that when clicked calls a code behind function. The function does some evaluation, and then I want to call javascript from within this asp.net function.

Best Answer

While pranay's answer is correct in the function call, the rest is off, here's hopefully a better explanation:

You can use ClientScript.RegisterStartupScript() to do what you want, like this:

void myButton_Click(object sender, EventArgs e)
{
  var script = "alert('hi');";    
  ClientScript.RegisterStartupScript(typeof(Page), "ButtonAlert", script, true);
}

The format is (type, scriptKey, scriptText, wrapItInScriptTags).

If you are operating with an UpdatePanel, it's very similar, except you need to use the slightly different ScriptManager.ResgisterStartupScript(). Use the UpdatePanel as the control and type parameters in that case to be safe.

Do:

var isTrueSet = (myValue === 'true');

using the identity operator (===), which doesn't make any implicit type conversions when the compared variables have different types.

Don't:

You should probably be cautious about using these two methods for your specific needs:

var myBool = Boolean("false");  // == true

var myBool = !!"false";  // == true

Any string which isn't the empty string will evaluate to true by using them. Although they're the cleanest methods I can think of concerning to boolean conversion, I think they're not what you're looking for.

Javascript – var functionName = function() {} vs function functionName() {}

The difference is that functionOne is a function expression and so only defined when that line is reached, whereas functionTwo is a function declaration and is defined as soon as its surrounding function or script is executed (due to hoisting).

For example, a function expression:

// TypeError: functionOne is not a function
functionOne();

var functionOne = function() {
  console.log("Hello!");
};

And, a function declaration:

// Outputs: "Hello!"
functionTwo();

function functionTwo() {
  console.log("Hello!");
}

Historically, function declarations defined within blocks were handled inconsistently between browsers. Strict mode (introduced in ES5) resolved this by scoping function declarations to their enclosing block.

'use strict';    
{ // note this block!
  function functionThree() {
    console.log("Hello!");
  }
}
functionThree(); // ReferenceError

Best Answer

Related Solutions

Javascript – How to convert a string to boolean in JavaScript

Do:

Don't:

Javascript – var functionName = function() {} vs function functionName() {}

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