Table of Contents
grammar
rule
Example 3
Default parameters in JavaScript
Illustrating parameter type and argument type
Illustrating number of arguments and parameters in a function
Home Web Front-end JS Tutorial What are the basic rules for JavaScript parameters?

What are the basic rules for JavaScript parameters?

Aug 22, 2023 pm 05:13 PM

What are the basic rules for JavaScript parameters?

In this tutorial, let’s discuss the basic rules of JavaScript parameters.

JavaScript functions are codes that perform specific tasks. Function arguments are a list of names from the function definition. Parameters are also called formal parameters or formal parameters.

We can declare parameters according to the following syntax.

grammar

function functionName(param1, param2)
{
}
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When a parameter has no value, the default value will be used.

rule

  • Declare default parameters as final parameters to avoid errors.

  • JavaScript function definition does not specify parameter types.

  • JavaScript functions do not check the type of input parameters.

  • JavaScript functions do not check the number of input parameters.

The Chinese translation of

Example 1

is:

Example 1

The following program declares the default parameters of a function. Therefore, when there are no parameter values, the function assumes the default value.

<html>
<body>
   <h2 id="Default-parameters-in-JavaScript">Default parameters in JavaScript </h2>
   <p> <b> Input = Sum(10) </b> </p>
   <p> <b> Input = Sum(10,30) </b> </p>
   <div id="paramDefBtnWrap">
      <button id="paramDefBtn"> Run </button>
   </div>
   <p id="paramDefOut"> </p>
   <script>
      var paramDefOut = document.getElementById("paramDefOut");
      var paramDefBtnWrap = document.getElementById("paramDefBtnWrap");
      var paramDefBtn = document.getElementById("paramDefBtn");
      var paramDefInpStr = "";
      paramDefBtn.onclick = function() {
         
         //paramDefBtnWrap.style.display = "none";
         function sum(param1, param2 = 20) {
            var sum = param1 + param2;
            paramDefInpStr += param1 + " + " + param2 + " = " + sum + "<br><br>";
         }
         sum(10);
         sum(10, 30);
         paramDefOut.innerHTML = paramDefInpStr;
      };
   </script>
</body>
</html>
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The Chinese translation of

Example 2

is:

Example 2

The following program accepts an integer parameter and a string parameter input. The output returns 'NaN' because the function did not check the parameter types.

<html>
<body>
   <h2 id="Illustrating-parameter-type-and-argument-type"> Illustrating parameter type and argument type</h2>
   <p> <b> Input = Multiply(10, 'ten') </b> </p>
   <div id="paramArgBtnWrap">
      <button id="paramArgBtn"> Run </button>
   </div>
   <p id="paramArgOut"> </p>
   <script>
      var paramArgOut = document.getElementById("paramArgOut");
      var paramArgBtnWrap = document.getElementById("paramArgBtnWrap");
      var paramArgBtn = document.getElementById("paramArgBtn");
      var paramArgInpStr = "";
      paramArgBtn.onclick = function() {
         
         //paramArgBtnWrap.style.display = "none";
         function mult(param1, param2) {
            var prod = param1 * param2;
            paramArgInpStr += "Argument 1 type is " + typeof(param1) + "<br><br>";
            paramArgInpStr += "Argument 2 type is " + typeof(param2) + "<br><br>";
            paramArgInpStr += param1 + " × " + param2 + " = " + prod + "<br><br>";
         }
         mult(10, 'ten');
         paramArgOut.innerHTML = paramArgInpStr;
      };
   </script>
</body>
</html>
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The Chinese translation of

Example 3

is:

Example 3

The following program has three parameters and four parameters. The length property of ‘arguments’ objects and functions differentiates them for us.

<html>
<body>
   <h2 id="Illustrating-number-of-arguments-and-parameters-in-a-function"> Illustrating number of arguments and parameters in a function</h2>
   <p> <b> Input = 1, 'one', Date, {} </b> </p>
   <div id="infArgBtnWrap">
      <button id="infArgBtn"> Run </button>
   </div>
   <p id="infArgOut"> </p>
   <script>
      var infArgOut = document.getElementById("infArgOut");
      var infArgBtnWrap = document.getElementById("infArgBtnWrap");
      var infArgBtn = document.getElementById("infArgBtn");
      var infArgInpStr = "";
      infArgBtn.onclick = function() {
         
         //infArgBtnWrap.style.display = "none";
         function argFunction(arg1, arg2, arg3) {
            infArgInpStr += "Function Parameters = " + argFunction.length + '<br><br>';
            infArgInpStr += "Function Arguments = " + arguments.length + '<br><br>';
            infArgInpStr += "Arguments are, <br><br>"
            for (i = 0; i < arguments.length; i++) {
               infArgInpStr += argFunction.arguments[i] + "<br>";
            }
            infArgOut.innerHTML = infArgInpStr;
         }
         argFunction(1, 'one', Date, {});
      };
   </script>
</body>
</html>
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This tutorial teaches us the basic parameter rules. Be sure to declare a default parameter value to avoid errors. Pay attention to parameter types and parameter value types when coding. Be careful to follow the parameter order.

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