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Introduction to AngularJs expressions

AngularJS Expressions are like small JavaScript code that can be written in HTML view using interpolations (double curly braces) and the AngularJS directive as an attribute of the directive. AngularJS resolves these expressions and returns the result exactly at the place where the expression was written. These expressions can be String literals, operators, or variables. AngularJS expressions are just like JavaScript expressions but with few Enhancements.

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Syntax

Using in HTML view

Using Expressions as operators

Using Expressions as literals/variables

How do Expressions work in AngularJS?

In Expressions are Just like JavaScript, small code snippets evaluated directly in HTML view using either interpolations or directive attributes. These expressions are always binded to the scope of the HTML and cannot be evaluated outside the scope. Expressions can contain literals, operators, variables, or directive attributes where a function can be called to evaluate the expression.

Another way of using AngularJS expression with complex logic is by making a function call from the HTML view and defining the function in the controller. $eval () method can be directly used in the HTML view to evaluate your expression

Some Limitations of expressions are:

AngularJS Expressions cannot be any conditional or looping statements

AngularJS Expressions doesn’t permit declaring a function

Regular Expressions cannot be used with Expressions (use ng-patter instead)

New Object creation cannot be done inside Expression

Comma, Void, or bitwise Operators cannot be used in Expression

Examples of AngularJs expressions

Here we discuss the following examples mention below

Example #1

Using Operators as AngularJS Expressions

Index.html

Addition Result is {{firstNumber + secondNumber}} Subtraction Result is {{firstNumber – secondNumber}} Multiplication Result is {{firstNumber * secondNumber}} Division Result is {{firstNumber / secondNumber}}

chúng tôi

angular.module('app', []) .controller('ExpressionsController', function ($scope) { $scope.operators = ["Add", "Subtract", "Multiply", "Divide"]; });

The above example shows how easily expressions are used in an HTML view to evaluate Operators and return the result exactly at the place where the expression is written.

Here input type number is used to accept the first number firstNumber from the user.

Here input type number is used to accept the second number secondNumber from the user.

Here, dropdown gives different operation options to users like add, subtract, multiply, and divide.

Based on which Operation is selected from the Dropdown, That operation is evaluated in an expression.

Output:

Output 1: Enter First and Second Number

Output 2: Select Add Operator and check Addition Result

Output 3: Select Multiply Operator and Validate Multiplication Result

Output 4: Select Divide Operator and Validate Division Result

Example #2

Using Operators as Expressions

Index.html

Final Result is {{finalVal}}

chúng tôi

angular.module('app', []) .controller('ExpressionsController', function ($scope) { $scope.operators = ["Add", "Subtract", "Multiply", "Divide"]; $scope.evaluateExpression = function () { if ($scope.selectedOp === 'Add') { $scope.finalVal = $scope.firstNumber + $scope.secondNumber; } if ($scope.selectedOp === 'Subtract') { $scope.finalVal = $scope.firstNumber - $scope.secondNumber; } if ($scope.selectedOp === 'Multiply') { $scope.finalVal = $scope.firstNumber * $scope.secondNumber; } if ($scope.selectedOp === 'Divide') { $scope.finalVal = $scope.firstNumber / $scope.secondNumber; } } });

Here input type number is used to accept the first number firstNumber from the user.

Here input type number is used to accept the second number secondNumber from the user.

Once the result is evaluated, the final value can be seen here

Output 1: Enter First and Second Number

Output 2: Select Add Operator and check Addition Result

Output 3: Select Multiply Operator and Validate Multiplication Result

Output 4: Select Divide Operator and Validate Division Result

Conclusion

AngularJS Expressions are very useful in the application, which comes with many pros and cons. It makes the small script coding easier as it can be directly done in the HTML view as well as complex logic can be evaluated in the controller. There are different types of expressions and will always be used in Apps, so knowing them is a must.