Set Value

The setValue task allows setting a value to environmental variables (e.g., variables stored in the global object). It is useful for implementing experiment conditions.

API

Only one of value, valueFromVariable and fn can be used.

Basic use

Following are a set of examples for the basic use of the setValue task, below are some more advanced applications.

In the following example, we set the value ‘condition1’ into the variable cond within the global object.

{
    type:'setValue',
    variableName:'cond',
    value:'condition1'
}

It is possible to assign nested variable names. In the following example, we set the value of the variable isControl within the global.conditions object.

{
    type:'setValue',
    variableName:'conditions.isControl',
    value:true
}

You can also copy variables. In the following example, we copy the user’s response to a questionnaire into a variable under global

{
    type:'setValue',
    variableName:'conditions.hasConsent',
    valueFromVariable: 'consent.questions.consent.response'
}

You can also create variables dynamically, using a function. The global object is the function’s argument:

{
    type: 'setValue',
    variableName: 'score',
    fn: function(global){
        return global.score1 + global.score2;
    }
}

Finally, the task allows posting the variable and its value to the server (i.e., logging it):

{
    type:'setValue',
    variableName:'cond',
    value:'condition1',
    post:true
}

Experimental conditions

Following, are two examples for the use of setValue in order to manage multiple experimental conditions.

In this example, we use a “choose” mixer to choose an experimental condition. We set the selected condition to global.condition and even send it to the server (post:true).

{
    mixer: 'choose',
    data: [
        {
            mixer: 'wrapper',
            data: [
                {type:'setValue', variableName: 'condition', value: 'trueInstructions', post:true},
                {type:'message', template: 'These are the true instructions', keys: ' '}
            ]
        },
        {type:'setValue', variableName: 'condition', value: 'control', post:true},
    ]
}

Sometimes it is more convinient to separate the randomization from actually running the tasks. In this example, we use a “weightedChoose” mixer in order to randomize the global.condition variable, so that there is twice the probability to be in the ‘trueInstructions’ group than in the ‘control’ group. We then use a branch mixer in order to choose the appropriate instructions.

[
    // Randomization
    {
        mixer: 'weightedChoose',
        weights: [2,1],
        data: [
            {type:'setValue', variableName: 'condition', value: 'trueInstructions', post:true},
            {type:'setValue', variableName: 'condition', value: 'control', post:true}
        ]
    },
    // Execute appropriate task (or not...)
    {
        mixer: 'branch',
        conditions: {compare: 'global.condition', to: 'trueInstructions'},
        data: [
            {type:'message', template: 'These are the true instructions', keys: ' '}
        ]
    }
]