Is the 'type' attribute necessary for <script> tags?

Question

For HTML 4.x, the type attribute is required. Source

This attribute specifies the scripting language of the element's contents and overrides the default scripting language. The scripting language is specified as a content type (e.g., "text/javascript"). Authors must supply a value for this attribute. There is no default value for this attribute.

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For HTML 5, it is optional. If it is not specified, it defaults to text/javascript. Source

The type attribute gives the language of the script or format of the data. If the attribute is present, its value must be a valid MIME type. The charset parameter must not be specified. The default, which is used if the attribute is absent, is "text/javascript".

Recommendation: See HTML 5.2

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For HTML 5.2, it should be omitted if using a valid JavaScript MIME type (e.g. text/javascript). Source

Omitting the attribute, or setting it to a JavaScript MIME type, means that the script is a classic script, to be interpreted according to the JavaScript Script top-level production. Classic scripts are affected by the charset, async, and defer attributes. Authors should omit the attribute, instead of redundantly giving a JavaScript MIME type.

in HTML5 you do not need the type attribute, but in HTML<=4 and (X)HTML it should be declared

The HTML 5.2 standard (late 2017) says you should omit the type attribute.

The type attribute allows customization of the type of script represented:

Omitting the attribute, or setting it to a JavaScript MIME type, means that the script is a classic script, to be interpreted according to the JavaScript Script top-level production. Classic scripts are affected by the charset, async, and defer attributes. Authors should omit the attribute, instead of redundantly giving a JavaScript MIME type.

(emphasis mine.)

Source: https://www.w3.org/TR/html52/semantics-scripting.html#element-attrdef-script-type

For testing purposes it WILL work without effect, but W3C requires it to validate correctly. The HTML 5 draft doesn't call for it as a requirement, but that is still in draft form at the W3C and they aren't recommending it.

Any browser that matters will parse it fine though.