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Kabue Charles
Kabue Charles

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TypeError: Assignment to read-only properties is not allowed in strict mode

By a show of hands, how many knew that HTMLElement.style is readonly?

Styles should not be set by assigning a string directly to the style property (as in element.style = "color: blue;"), since it is considered read-only, as the style attribute returns a CSSStyleDeclaration object which is also read-only.

Anyway, element.style = "color: blue;" will give you the following error in strict mode:

TypeError: Assignment to read-only properties is not allowed in strict mode

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typescript

11 Tips That Make You a Better Typescript Programmer

1 Think in {Set}

Type is an everyday concept to programmers, but it’s surprisingly difficult to define it succinctly. I find it helpful to use Set as a conceptual model instead.

#2 Understand declared type and narrowed type

One extremely powerful typescript feature is automatic type narrowing based on control flow. This means a variable has two types associated with it at any specific point of code location: a declaration type and a narrowed type.

#3 Use discriminated union instead of optional fields

...

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