JavaScript Language | 30 Minute Test

All these facilities are available in JavaScript. Additionally, all development environments provide syntax to create and use memory variables, constants, and functions.

In order to load a page, the browser must parse the contents of all script tags, which adds additional time to the page load. By minimizing the amount of JavaScript needed to render the page, and deferring parsing of unneeded JavaScript until it needs to be executed, you can reduce the initial load time of your page.

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JavaScript code is as easy to be implemented and run. It can be called by using a function or a method.

When the result of a numeric operation is larger than the largest representable number (overflow), the result is a special infinity value, which JavaScript prints as Infinity. Similarly, when a negative value becomes larger than the largest representable negative number, the result is negative infinity, printed as -Infinity. The infinite values behave as you would expect: adding, subtracting, multiplying, or dividing them by anything results in an infinite value (possibly with the sign reversed).

A non-string can be converted in two ways without using a new operator. false.toString() and String(false).

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An invocation expression is JavaScript’s syntax for calling (or executing) a function or method. It starts with a function expression that identifies the function to be called.

L-value is a historical term that means “an expression that can legally appear on the left side of an assignment expression.‿ In JavaScript, variables, properties of objects, and elements of arrays are lvalues.

JavaScript is not a full-blown OOP (Object-Oriented Programming) language, such as Java or PHP, but it is an object-based language.

A statement block is a block that combines more than one statements into a single compound statement for ease.

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The do/while loop is less commonly used when compared to the while loop. Here, it prints from the array in the given order.

Before each iteration, the interpreter evaluates the variable expression and assigns the name of the property (a string value) to it.

use strict is a directive introduced in ECMAScript5. Directives are not statements because it does not include any language keywords. Also, it can appear only at the start of a script or at the start of a function body, before any real statemenst have appeared.

An object is an unordered collection of properties, each of which has a name and a value. Property names are strings, so we can say that objects map strings to values.

When using square bracket notation, the expression inside the square brackets must evaluate to a sting or a value that can be converted to a string.

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If you omit a value from an array literal, the omitted element is given the value.

The reverse() followed by a join() will reverse the respective array and will store the reversed array in the memory.

The typeof property is used to identify the array type.

The function definitions begin with the keyword function followed by an identifier that names the function and a pair of parantheses around a comma-separated list of zero or more identifiers.

If the return statement does not have an associated expression, it returns the undefined value.

Another way to write o.m(x,y) is o[“m‿](x,y).

Even if the string value passed as a parameter to eval does represent a numeric value the use of eval() results in an error being generated.

The parseInt() function returns the first integer contained in the string or 0 if the string does not begin with an integer.

The code above creates 10 closures, and stores them in an array. The closures are all defined within the same invocation of the function, so they share access to the variable i. When constfuncs() returns, the value of the variable i is 10, and all 10 closures share this value. Therefore, all the functions in the returned array of functions return the same value.

Like most modern programming languages, JavaScript uses lexical scoping. This means that functions are executed using the variable scope that was in effect when they were defined, not the variable scope that is in effect when they are invoked.

Dynamically generating graphics from real-time data uses a lot of CPU cycles.

Lexical scoping is standardized in all algorithmiJavaScript Languages (ALGOL), such as Ada, Pascal, and Modula2. Additionally, it is used in modern functional languages like ML and Haskel.