The variable 'this' is not recognized within the foreach loop

Question

The variable 'this' is not recognized within the foreach loop

While working on my TypeScript code and iterating through an array, I encountered an issue with accessing the 'this' object. Here's a snippet of the code:

console.log('before iterate, this = ' +this);
myarray.days.forEach(function(obj, index) {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
});

Unfortunately, the code fails because 'this' is undefined within the loop. Despite correctly printing as [object object] outside the loop, it becomes undefined inside. What could be causing this behavior? How can I fix it?

typescript typescript2.0 typescript1.8

Answer 1

Answer №1

To solve the issue of maintaining the correct 'this' scope in JavaScript, you have two options:

myarray.days.forEach((obj, index) => {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
});

Alternatively, you can use the bind method:

myarray.days.forEach(function(obj, index) {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
}.bind(this));

The issue arises when passing a regular function as a callback, leading to the loss of the intended 'this' context. By utilizing arrow functions or the bind method, you ensure that the correct 'this' scope is maintained for future executions.

Answer 2

To solve the issue of maintaining the correct 'this' scope in JavaScript, you have two options:

myarray.days.forEach((obj, index) => {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
});

Alternatively, you can use the bind method:

myarray.days.forEach(function(obj, index) {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
}.bind(this));

The issue arises when passing a regular function as a callback, leading to the loss of the intended 'this' context. By utilizing arrow functions or the bind method, you ensure that the correct 'this' scope is maintained for future executions.

Answer 3

Answer №2

Include the this as an argument for the callback function.

Replacing }.bind(this)); with }, this); is a possible solution to the issue in Angular.

Therefore, your code snippet should appear as follows:

myarray.days.forEach(function(obj, index) {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
}, this);

Answer 4

Include the this as an argument for the callback function.

Replacing }.bind(this)); with }, this); is a possible solution to the issue in Angular.

Therefore, your code snippet should appear as follows:

myarray.days.forEach(function(obj, index) {
    console.log('before transform, this : ' + this);
    this.datePipe.transform...
}, this);

Answer 5

Answer №3

Give this a shot:

myarray.days.forEach( (obj) => {
    console.log('prior to transformation, this : ' + this);
    this.datePipe.transform...
});

Answer 6

Give this a shot:

myarray.days.forEach( (obj) => {
    console.log('prior to transformation, this : ' + this);
    this.datePipe.transform...
});

The variable 'this' is not recognized within the foreach loop

Answer №1

Answer №2

Answer №3

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