Promises in Typescript

Promises are used to wait for a function to get executed and return the value. Once the value is returned, it will execute the next statements.

Single Promise function in Typescript


console.log("Instruction 1");
console.log("Instruction 2");
apiCall().then((result) => {
    console.log(result);
    console.log("Instruction 4");
    console.log("Instruction 5");
});

function apiCall(): Promise<string> {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve("Instruction 3");
        }, 3000);
    });
}

Cascading promise function in Typescript


console.log("Instruction 1");
console.log("Instruction 2");
apiCall().then((result) => {
    console.log(result);
    apiCall2(result).then((result) => {
        console.log(result);
        console.log("Instruction 4");
        console.log("Instruction 5");
    })
});

function apiCall(): Promise<string> {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve("Instruction 3");
        }, 3000);
    });
}

function apiCall2(param: string): Promise<string> {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve(param);
        }, 3000);
    });
}

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