The typeof operator returns a string indicating the type of the operand's value.

The <feSpotLight> SVG filter primitive defines a light source that can be used to create a spotlight effect. It is used within a lighting filter primitive: <feDiffuseLighting> or <feSpecularLighting>.

The <feTurbulence> SVG filter primitive creates an image using the Perlin turbulence function. It allows the synthesis of artificial textures like clouds or marble. The resulting image will fill the entire filter primitive subregion.

This page lists features of JavaScript that are deprecated (that is, still available but planned for removal) and obsolete (that is, no longer usable).

The JavaScript exception "reduce of empty array with no initial value" occurs when a reduce function is used.

The JavaScript exception "can't set prototype of this object" occurs when attempting to set the prototype of an object, but the object's prototype is frozen, either by being a built-in immutable prototype object, or by being non-extensible.

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Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it somewhere in the scope from which you wish to call it.

JavaScript is a prototype-based language — an object's behaviors are specified by its own properties and its prototype's properties. However, with the addition of classes, the creation of hierarchies of objects and the inheritance of properties and their values are much more in line with other object-oriented languages such as Java. In this section, we will demonstrate how objects can be created from classes.

This chapter introduces how to work with strings and text in JavaScript.