Expressions

Expressions are a feature of Angular. They are a subset of JavaScript commands in addition to some Angular function. Expressions are used in many places in Angular. For example, anytime you bind data, you can use an expression. This makes understanding expressions important.

An expression will be evaluated to a value, to a true statement, to a function in scope, or to a variable in scope. This makes them powerful, but they do have some limitations.

Expressions in JavaScript

You can use some JavaScript, but not all JavaScript in an expression. Here are some of the things that you can and cannot do in JavaScript using expressions:

  • You can use a string, number, Boolean, array literal, or object literal
  • You can use any operators, for example, a + b, a && b, or a || b
  • You can access properties on an object or look up values in an array
  • You can make function calls
  • You cannot use flow control statements in an expression, for example, an if statement

Context

When an expression is evaluated in Angular, it will use the scope that it is in. This means that you can use any object or function that is accessible in the scope. One difference is that you will not get access to the global window. For example, you will not be able to use window.alert in an expression.

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